It would be semi-limited to prevent people using econ or TTH. If Maximus is limited to 1, people just replace it with Rooklord while they still can play econ or TTH
Semi-limiting maximus will not balance Koa'ki Meiru at all, Koa'ki don't really care about TTH (3×floodgates and 3×canadias are more than enough), 2 Maximuses with balance aren't a big issue at all, nerfing this deck without killing it will not be easy.
I'm only talking about balance Koa'ki.
This is definitely the boss monster, but limiting it doesn't 🔥 the deck. At worst makes it more vulnerable to Spellbook decks, but those are on the decline.
I'd hit Sandman to weaken this decks backrow protection. Slows down this decks ability to setup it's OTK.