In what way does Ex3 fundamentally differ from Ex2 such that the assumption that different splats would have different contexts no longer holds? I mean, sure, Ex3 doesn't have any splats except Solars at the moment so I can't specifically point to any examples thereof, but as expectations go, this is a very reasonable assumption, since if that assumption no longer holds we've, uh, got bigger problems than martial arts, man.
I'm not sold on the reasonableness of this expectation, depending on what we have in mind with "contexts." I don't expect 3e to go the M&M route of "everything is just refluffing on the exact same powers," but...
Let me try to talk through this. So, the go-to examples for how things break in 2e are things like perfect defense interactions - which are not a thing in the same way, in 3e. Or, like, "I ignore all bashing damage, I convert all lethal to bashing, I punch everything within line of sight?" I'm not betting on seeing those recur, either.
And those are just specific examples - sure. But more broadly, I think 3e has fewer of what we might think of as game-changer powers: powers that fundamentally alter how you relate to the world at large,
particularly in a way that's spammable. Its powers tend to be more, like... get a finite number of extra attacks. Roll a finite number of extra dice. Treat one of the faces of your dice differently. Make a counterattack under such-and-such conditions.
I'm not saying those can't break a game. But I
am saying they're easier to, mm,
box up, in a way that "How does this interact with a Solar's ability to ignore the next twenty attacks?" or "How does this interact with a Lunar's power to refuse to die?" or the general theme of 2e's WHOA MAN DID YOU SEE THAT CHARM powers were not. You can crack Magic wide open by abuse of +1/+1 counters, but it's going to be harder for that to sneak up on you if the prevalence of weird this-card-only textual descriptions has gone way down.
So when martial arts is mostly adding things of that form ("You get +1 Defense! It doesn't break caps" "You get double-7s in very narrow circumstances, which doesn't stack with your native Charms!"), I mean, that
does feel kind of containable in a way 2e did not.
I get that this sounds like intuition and fuzzy handwaving, and that's because, as you note, we have no other splats; intuition and hand-waving are all I can possibly offer. I will not be shocked if this does not work for 3rd at all, and the whole thing's a terrible mess.
But surely that's not a logical necessity.
Certainly, we don't know that yet. But, uh, we aren't specifically talking about 3E, so why are you attempting to use "3E doesn't have any splats yet to evaluate charmshare"?
What
are we specifically talking about? It surely isn't 2e. If it isn't specifically 3e, what is it? A hypothetical alterna-rebuild-from-first-principles?
Seems to be recurring.
Intended to be a constraint on the use of high mote cost charms in a charmset which had no cheap spammable low-tier effects
I would not bet on this. I'll be surprised, given how Solars have gone, if Sids don't end up with, say, at least 3x as many Charms as their 1e sets, probably including some spammable low-cost things.
and no way to make custom charms,
This is true.
and was very reliant on expensive scenelongs on top.
This, who knows?
Classic 1E example: Impeding the Flow (3m) vs Dipping Swallow Defense (2m), Serenity in Blood (5m 1w) vs Heavenly Guardian Defense (3m 1w). Both parry charms are qualitatively superior to their Solar equivalents (DSD generated a full pool parry out of the ether, ItF parried any parriable attack. Serenity in Blood had a built-in surprise negator on top of being Heavenly Guardian, Heavenly Guardian was just Heavenly Guardian), but you had a tiny mote pool, so you'd generally lose by attrition even if you had outright better charms because they were so comparatively expensive.
But that example doesn't work at all, anymore, because the
Solar Charms have major weird restrictions. HGD isn't even (usually) a perfect defense, and even as a partial defense, it's hideously expensive. SSE is once per scene and high-priced. AST is usually just some Decisive soak. What does the Sidereal context look like, if that's the vanilla option?
If we evaluate the whole affair by the 3e Sidereal Excellency, Sid Charms are likely to be cheaper and more efficient than their Solar counterparts. That's probably a terrible metric, but we don't really have a
good one right now. And that's all I'm really trying to say: there are varying,
reasonable hypotheses about what happens next, and very different conclusions follow logically from them.