No, he's not. He's one of the oldest. That's it.
In canon, Ma-Ha-Suchi was a debutante, a hedonistic socialite of the First Age whose driving goal in life was to sleep around with as many of his peers as he could. When the Deliberative fell, he survived by hiding in the Wyld, mutating and twisting until he almost became a Chimera. After the Balorian Crusade was defeated, he crept back into the world and decried the rebuilding efforts as a waste of time. "Civilisation was a mistake," he said, preferring to squat in the grim ruin of his ancient manse at the head of a braying horde of barbarians and beastmen, raping and pillaging the surrounding area without point or purpose.
Fundamentally, canon Ma-Ha-Suchi has done. Nothing. He's not a 'Great Lunar', he's a waste of an Exaltation. He's a shallow putz taking out his own self-hatred on the world because he can't get over himself. It is literal canon that he is stuck in a centuries-old temper tantrum because he's not pretty anymore. He's not even a character, he's a dungeon end-boss with as much nuance as a random encounter from D&D.
Yes, TAW's take on Ma-Ha-Suchi is a monster who wants to tear down the world. But at least he's a monster with some degree of agency, of competence, of purpose. He exists to show the dark side of the Terrifying Argent Witches, how they can play the monster so well because they are monsters. Terrible things existing outside society, in the liminal between-spaces of the world, needed but never liked. And it's okay for him to do that because TAW offers a bountiful spread of other NPC's to show that Lunars can also be great. Ma-Ha-Suchi has never been a great Lunar - but in contrast to canon, TAW doesn't expect him to be a great Lunar. That's what Raksi, or Koworai Suhal, or Nekay Pai are for.
I don't get the impression that first age MHS was particularly useless, though second age MHS may regard his previous self with a level of self hatred, he's been through a lot. He was obviously a hedonist, but if you read, say, DoTFA's comics, you can also see the start of what he would later become there. "No mercy to apostates" etc.
Clearly, while he was a hedonistic socialite who liked to sleep around, the merciless being he would one day become lurked beneath his handsome skin.
This is the problem with Lunars in a nutshell, rather than with Ma Ha Suchi. There's a fundamental dissonance between the idea of three hundred some celestial exalts still being free and able to do stuff, and the fact they haven't really changed the world that much. 3rd edition seems to be trying to address this, but I feel like the correct approach is to completely change the depiction, rather than in any way double down on it.
I don't want to step on what's obviously a much loved homebrew, especially one that I haven't had chance to really engage with. However, I don't find Ma Ha Suchi being the devil to be particularly compelling. I'd prefer to dial back his self hatred and make him be someone who now mostly disregards subtlety. Perhaps having failed to make headway with it several times over his long existence, and no longer being so suited for it as he once was. Rather than wanting to tear down society, I see him as being a wolf that wishes to build an empire, and is building the tools to do that.
The entire point of the Wyld Hunt is to kill Solars before they snowball and keep Lunars out. The conceit of the start date is that the Realm no longer has the available manpower to kill you specifically once you display an anima flare anywhere close to where they can mount a military expedition because a) their resources are being pulled back for the civil war buildup and b) there are 300 Solars respawning now, not a handful.
Yurgen has neither of the above applicable, so it's not particularly terrible to have him get wiped out by Wyld Hunt Round 2: We Take Our Jobs Seriously.
Because the (Sidereal-backed) Wyld Hunt is dangerous enough to kill Celestials and scary enough to deter many of the ones it doesn't kill.
As demonstrated by Sidereals killing the Bull.
Also, because Celestials who try to wreck the Realm usually get less lucky than the Bull.
I don't really like this approach either, because it kind of throw's solars under the bus in order to avoid throwing lunars under the bus.
The Bull of the North serves a good story purpose, which is to show that the Solars coming back is a big thing, and that they're going to change the world. Him then getting assassinated, especially if you're going to keep in the destruction of several realm legions at his hands feels like a very anti-climatic way to end that story, and one that actually goes against things as they've been established.
The problem, and this brings us back to Ma Ha Suchi, is that there's always been a tension within Exalted between the fact that solars are coming back and that's a big thing, and the fact that Lunars have been free for the whole length of the Shogunate and the Realm, and yet have not managed to really do that much.
3rd edition's background goes a way to address this by implying that there's sort of a long stalemate going on between the two sides, but it feels necessary to figure out how that works, and how to balance portraying the solar's return as significant while not removing any lunar influence on the setting.
I don't have time to write up a long treaties on how I'd do this, but I think my approach would be to make sure that Solar and Lunar mass combat charms are decisively different from one another, and to change the ratio of realm troops vs. local troops (which would fit my conception of how the realm mostly works on religion and food), and to have the Bull's attack be in a region without substantial lunar influence so the realm was just surprised by it.
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