Mearsheimer can be a bit too convincing for his own good, surely. What he has argued that is certainly convincing is that Russia was ready to negotiate a peace at the start of the war, when Russians and Ukrainians met in Belarus and then in Istanbul. If Putin wanted to recreate Imperial Russia, or the Soviet Union, then why would he negotiate for peace?
That's Mearsh's argument, which he articulates, e.g. here in Lex Friedman's show (sorry, I couldn't find a better source):
https://youtube.com/watch?v=r4wLXNydzeY&t=2684
Full transcript here: