Going through this blind on Tactician and having just reached act 3, I think most of this is really just a 5E balancing thing + some gear and class features being really REALLY busted more than anything else. But more 5E - even Solasta was also consistently in joke tier difficulty unless you played on the hardest difficulty there, which apparently doubled enemy stats (and gave them extra damage die from what I hear).

I think one of the major issues is that there aren't actually that many spellcasters or enemies using any actual threatening special abilities once you leave act 1. It felt like there were way more varied encounters in act 1. For all the crap we put this forum through pre-release arguing for a proper reaction system, I haven't even found that much reason to use counterspell or even have Gale use Shield at all because there were so few spellcasters with actual threatening spells or anyone actually targeting Gale.