I seriously cannut undrestand how anyone can think fights too difficult. Sometimes you mess up or yopur dice do. The stupid shove can do you in but even though i know how D&D works i played most of the fight without even CCing. Just plain hitting stuff and casting DD spells. But thats just me. Some fights are really designed bad.
Ragarding casters. Larian changed some rules. Shove gives melees basically an extra attack that can instakill if done right. Casters usually miss the skills and stats to shove successfully. Apart from that do the enemies succeed on lots more saves than i would expect given their saves and my characters spell DC. NPCs are created like PCs so every guardsman is a hero. D&D usually does not do that.
We are missing some INT and WIS feats too. They changed 5e too much to work properly anymore. With all the magic items, mostly weapons, the melee classes get way ahead of casters. D&D spellcasting is desiged to have lots of impace with few casts. Not working very well in the game. Stealth is not working well either.
Don't get me wrong, i like the game. I have 800+ hours. Funny enough 600 of them are in EA. After finishing 2 playthroughs i stopped after an hour into the 3rd. Says a lot i think. Expectations only partly met. I hope the future brings remedies. I am not a big fan on modding.
Sadly larian seems very stubborn regarding changes to their homebrew rules. Shove and jumping mechanic beeing a prime example. That messes up the whole D&D combat rules. Add a lot of barrels, ground effects and lots of more or less usefull/useless magic items and you have what we have now:
D&D themed DOS. Made me sad (even if i like the game otherwise).