Sorry if I sound rude, but from what I am reading, you don't come over as an experienced player in any way. At the very least not experienced with CRPGs, maybe MMOs?
1. The way itemization goes in DnD, it is your gear, that really makes you powerful. As in real life, you stick a long time with what you have. Later on the itemization becomes a problem, because you get ridiculously powerful. Apart from that you can get some pretty amazing gear in act 1, if you are actually thorough, like the Blood of Lathander, Aluvae, Light of Creation, Spellsparker and so on.
2. Character development depends a lot on your class, some are outright boring (which is not the same es weak), others offer stuff at pretty much every level and you have multiclassing, which is absolutely bonkers in this game. Dare I suggest investing more time in game mechanics and less in looting vases? Games like BG3 life from experimenting and respeccing is very, very cheap.
3. If anything the game is to easy. The battle you are mentioning is kinda annoying, but it is over in a few turns, if you actually use the mechanics available to you. The way to do this is sneak into a better position and make use of your skills. I'm pretty much a noob regarding these games but could do it second try. An experienced player should have no problem at all.
I mean, you have every right to be disappointed, but at least be it for real reasons and not because of overlooking most of the stuff while being "extreme thorough"
