Is a a good 4* better thsn a weak 5*?

So are there instances where you’re better off with a fully ascended 4* then a fully ascended 5*? I just got my 1st 5* blue and it’s Thorne. A pretty weak 5*. If I get him fully ascended, is he better than my fully ascended Grimm?

I would keep Grimm, but they serve different functions

Grimm has more utility due to defense debuff. I’d save your scopes for another 5* anyways. Perhaps you can pull Magni from TC20 if you’re training legendary.