Judging by the descriptions of artifacts and their picture, it does seem to be taking at least some cue from this style:
Yes, but... Okay, let's look at Daiklaves.
This description is from 1e, where they're more than four feet long and at least six inches wide. A four-foot-long sword, by the way, isn't obscene. Sure, it's about twice as long as your average katana, but it's about average for a European longsword (if we're including the hilt). The real sticking point is the six-inch width, which is twice as wide as William Wallace's
claymore at its widest point. It gives the thing the proportions of a snowboard. As far as I'm aware, there is no actual sword that has ever looked like this.
So we're talking about a sword with about three times of heft of your average longsword... which does, if you check the stats for 1e, a grand total of +1L damage. You see what I'm getting at, here? The dude with a cool looking normal sword just painted it gold and strapped
two more swords to its blade, for +1L damage. This is part of why daiklaves felt so trivialized, by the way - because they
were trivial. They were, as has been raised earlier, literally just Sword Of Swording +1, standard D&D loot. There's a reason 3e tries to get you to invest both personally and mechanically in a specific weapon.
It also means that the standard "heroic" sword is a big metal snowboard, which heavily implies that anyone who wants to play as one of the many, many anime characters who use non-absurd giant swords can go sit and swivel. Zorro, Sailor Venus, Kirito, Trunks (or Yajirobe), Signum, almost anyone
but Ichigo in Bleach... they're neglected, because the game is primarily interested in representing Cloud Strife and Zabuza. The latter is a fairly thinly-populated category, which becomes even thinner, relatively speaking, when you include all of the game's non-anime inspirations. Aragorn! We reforged the sword that broken! It's now bigger than Frodo.
I think that's a fair point, but I find your proposed solution lackluster.
Guts or Sephiroth don't spend limited power resources to wield their enormous weapons; they don't enter brief bursts of fury that are the only times when they can fully wield their powers. They can just wield oversized weapon as a matter of fact.
Not really true.
Sephiroth's weapon is oversized, but not
obscenely so. The Masamune is twice the length of a normal odachi, closer to a horse-killing zanbato... but that's only a little longer than a large claymore, and it's probably about as heavy. Its unwieldy length is pretty clearly meant to communicate his inhuman grace and dextrousness, and provide a deliberate contrast to Cloud's crude heavy strength-based weapon. It's no coincidence that it most resembles the overlong but strangely elegant sword of Sasaki Kojirou, while Cloud's weapon was inspired by Musashi's crudely-carved oar.
The Dragonslayer is specifically called out as being absurdly heavy, to the point that no-one but Guts could possibly wield it. When he does so, he's explicitly fueled by rage and ridiculous, unrelenting determination. The dude picks up Berserker Armour at some point just so he can keep going, and it eats into his stamina like no-one's business. It's true that Guts doesn't act as a burst-fighter, but that's because the story goes out of its way to point out all the reasons he
should be a burst fighter but can keep on going throughout the night because he
is/has Guts.
There are other examples where this comes out - Zabuza from Naruto is an ambush fighter, before that series went to DBZ-shit, and is scary because a) he can stealthily ambush you even with a giant sword, b) he'll be in-and-out before he even gets tired. Inuyasha's Tessaiga is normally a cool magic katana, but it acquires a massive shroud of energy or outright transforms into a giant sword when he pumps it with spirit energy. The same goes for Fate Testarossa's Bardiche, which is normally a fairly sensible polearm but transforms into an absurdly large energy sword when she burns energy (and armour) and goes all-out. Sanosuke in Rurouni Kenshin is
more dangerous when his ridiculous giant sword is broken, because even though he was strong enough to wield it, it was slowing him down.
And what is more important, this is not presented as a tactical decision - not in the sense that there are merits and drawbacks to using oversized weapons, and they're opening certain weaknesses in exchange for the benefits of their enormous reach and damaging power. They wield oversized weapon because they are able to, and being able to do it makes it automatically a superior choice. The Dragonslayer is the only way for a human-scale opponent to go toe to toe with the superpowered Apostles. There is no implication at any point that Cloud or Sephiroth would be just as powerful with smaller weapons, trading damaging power for the speed of a lighter weapon. If you can wield it, the oversized weapon is optimal.
I'm not sure I understand what you're saying, here. Guts with the Dragonslayer is explicitly slower than he was with his older, lighter but less powerful longsword - and fast, agile opponents are explicitly able to take advantage of that to strike at him, unless he's able to pin them down (like, say, getting stabbed through the cheek and biting down on their weapon, because HE'S GUTS oh god I miss Berserk). When Cloud wields shorter and lighter swords in Advent Children, he's notably faster and more agile than when lugging around his massive Buster Sword, capable of deflecting bullets.
Guts uses the Dragonslayer because it's suited to his fighting style and is the best weapon for him to take on giant, superhumanly tough enemies - not because a giant sword is just intrinsically superior in all ways. Hell, Cloud uses the Buster Sword basically for
sentimental value, remember.
Soulsborne characters - if they can wield their oversized weapon, they just can. They don't need to fuel it with magic, and they are not short-lived glass cannons who must expend huge amounts of power with every blow and be exhausted quickly.
wut
I can attack maybe three times in Dark Souls with my Greatsword before I become so puffed-out that I can't even block a zombie with a broken sword. In that same time span I can stab someone with my Rapier twice as often and still have Stamina left over - and that's not to mention what they do to my relative encumbrance values and ability to just dodge out of trouble. The counterbalance here is that my Greatsword
hits like a truck. This sells me on the idea that my huge awesome weapon which I swing like Guts does - all sweepy and devastating because I can barely handle the weight - is in fact a huge awesome weapon, and not an ornament piece with an anti-gravity module attached.
What doesn't betray the source material, then? Well, mostly, the "underwhelming" option as outlined by
@Revlid. Yes, it is something of a cop-out. But ultimately - in Bleach, powerful Shinigami can tank hits from Ichigo with minor injuries. Guts mows through hordes of mooks, but Apostles can take more than one of his blows. FF7 has heavily abstracted combat, but peripheral material shows Cloud having to hit opponents repeatedly, generally without causing gruesome wounds. Bosses can take several hits from an Ultra Greatsword.
I like your later point about how large weapons are often presented as an equalizer rather than dominator, but that's only relatively speaking - and in all the examples you're giving here, it's very clear that there's defensive magic at play.
Guts needs to hit (some, not all) Apostles more than once because they're giant monsters with tons of health levels - it would take a regular sword even more time to kill them, and whenever he hits anything without supernatural toughness (and a bunch of things
with supernatural toughness) it dies instantly. Cloud needs to hit Sephiroth a bunch of times in his final combo because he's some kind of weird Lovecraftian avatar - he doesn't even bleed each time he's hit, just explodes into smoke and feathers. Most of their fight consists of the two trying to not get hit - and when Cloud's hit, it's clearly a fight-ending injury until he gets the obligatory plot-tier edge-of-death pep-talk. The Shinigami in Bleach are specifically using their native magic to harden their skin, to the point where Kenpachi injures Ichigo's hands when he tanks his first attack.
I'm not sure how you could do that, in this context. Either you make daiklaves balanced with mundane weapons, at which point it's questionable why they exist, or not taking one for the sake of concept will be a deliberate weakness. There isn't much space in-between.
My favoured solution, again, is to make it so that daiklaves aren't the only supernaturally effective weapons out there.
They're certainly not in mythology or anime, not by a long shot.
Of course, this comes back to "but then we need to find something to distinguish a fuckhuge sword from a not-fuck-huge sword", and I plump for "the fuckhuge sword acts like a fuckhuge sword" and our opinion is split again because that means fuckhuge swords are as hard to use as fuckhuge swords, and they don't always seem that way in anime.