I didn't see the Moscovy doing too bad without my direct interference but, in general, AI cannot handle local autonomy and new rebel mechanics at all in the latest patch. And if a country expands a lot and haven't taken humanist ideas, rebels are overwhelming and can either collapse the country or exhaust its manpower, which will result into somebody declare war on it with snowballing consequences. And yes, dividing Tatars in subcultures contributes to that. Also, I've seen Ottomans collapse due to rebels more than once, same with Moscovy. On the other hand PLC is an unstoppable superpower after a new patch. Not only they have infinite manpower right off the bat now but I haven't seen any generals other than 3-star generals with stats like 5-6/5-6/*/* in droves for them without taking ANY military ideas in the XV century, they can just steamroll Moscovy if they decide to.