It is definitely time for a new game. There's already quite a few things confirmed in CK3 game that weren't remotely possible in CK2. And what more can they add to CK2 at this point? Sure, there can always be more content, but modders can (and inevitably will) do that better anyway. In terms of systems, all the things that people have been wanting the whole time either were wrapped up in Holy Fury (which was sort of a grab bag of things they'd been saying they wanted to do for years, or that were in CK1) or aren't really possible with the way the game is coded. On top of that there are things that don't really work that well but which they can't change too much because they were already sold to people as DLC features, like merchant republics and Muslim decadence. Sure, they could let CK2 sit a while without any update, but why?
When it comes to porting, I do think they should have gone through and ported many of the CK2 and CK1 events, where it makes sense to, and preferred to include rather than exclude. But many events either tie into specific systems that are being changed anyway, or were specific narratives that CK2 players have already experienced. It makes sense not to carry too much over.
As for whether it's a good sequel, that's still up for debate, but even if it's not, CK2 still exists and the price is only going down.
eu4 is better than eu3.
That's very subjective. It has gotten a lot of good support since launch, but it still relies very heavily on the core mana system. They may have polished that turd up a lot better than with HoI or Stellaris, but that doesn't mean it's better overall.