I get what it's based off, but it's still a Super Heavy tank based on appearances, and that doesn't fit with how Space Marines are used in the current setting. The first of those images (the fellblade) is from the Great Crusade when Space Marines operated as more traditional armies with thousands and thousands of Marines available, it fit in with them there. That isn't how chapters of around 1000 Marines operate in the 41st millenium, so having a super heavy available doesn't make much sense. There aren't going to be forces of Space Marines large enough to warrant the user of super heavy vehicles as they're aimed at more for quick strike missions.
Maybe if it was some sort of super-heavy transport for a full company of Marines that wouldn't be too bad, though.
Hey, Gman is back and he's bringing back the Crusade!
As for splitting the legions, well..
‘I should not have done it,' repeated Guilliman, gesturing expressively as he spoke. ‘I thought I was doing the right thing. I thought I was following the Emperor's wishes, letting men rule the affairs of men.'
And later others accuse him of building a new de-facto Legion; he stations a full ten chapters to guard Ultramar, but he denies that was his intent.
He is also accused of building up the Unnumbered Sons as a Legion, as they are a much larger force than a single chapter, but they are eventually broken up into a bunch of chapters.
By salty Governors whose planets were absorbed into the realm of Ultramar.