It's not that combats "aren't good" in BG3 according to me. There are a lot of spells and features, the "arena" are interresting even if I'd like more choke points and close combats, you can sometimes interract with the environment, the verticality matter...
...but yes, they aren't balanced at all and you're doing the same thing again and again...
They're not tactical, they're not deep at all and the difficulty becomes very easy really fast when you know a very limited numbers of things. The deepest thing to know in BG3 is backstab and highground... Hurra.
The first time you're playing it's +- ok but if you're not a noob tactical TB games player and/or someone that never played a D&D game before... It really becomes boring and unchallenging fast.
And higher level of difficulty won't change anything because the easiest things to know /understand in BG3 are also the most powerfull...
Oh yes you can also use the few other OP things or be "creative" with barrels so it becomes a real story mode.
On top of that we have "powers" our ennemy never use so we're very more powerfull than them ... Except when Larian add them frustrating powers to create a fake feeling of difficulty.... Hello minotaurs...