I feel you, in 5e it sometimes the rolls are plain against you.
HOWEVER since BG3 is NOT EXACTLY 5e, there are ways in which you can get around % chance to hit. But don't get me wrong, sometimes you just get screwed by Gil.
1. Use throwables for making puddles. Saving your caustic bulb and lighting it up can easily turn the battle in your favor...or you know, spend it all killing Command Zhalk and the mindflayer, i won't judge. Thanks to DoS2 (divinity original sin 2) I actually carry barrels of liquid with me at all times. Firewine, gunpowder, water.
2. Magic missile at lvl 2 + haste = a non 5e turn allowing 2 casts of mm2 for essentially 8d4+8 so roughly 24dmg avg. Doesn't seem like alot, but that burst helped the wizard who shall not be named and also cannot see in the dark.
3. Use dancing lights for MYSTRA'S SAKE! Your darkvision has its limited range, unless of course you are a drow warlock who likes to see in magical darkness. Lighting up the place increases your chance to hit.
4. Faire fire is really good especially when it procs from a certain mace. Having advantage on all attacks on the target can turn a 70% attack roll to a 100%.
5. ACID! If you can manage to force your enemies to stand in acid while they rip your face off in a fight which is considered a DEADLY encounter by CR standards, damned action economy, you will give them a -2 to AC, which is nothing to scoff at.
6. PRONE! I really hope Larian does not take away cantrips messing with puddles on the ground, because Frost bolt is a fantastic spell. Make the ground frozen and force a dex save on any enemy that walks through it. If they fail, they go prone, and thats good.
7. Let your waterdeep wizard die...alot. Im not kidding, i actually let him die in choke points since AI will not jump out of it.
8. And of course Distance, height, and backstab matter, but you all knew this already.
9. OH and you might have two really REALLY powerful poisons that can do 7d6 dmg 21avg per hit. Try using them.
In DoS2, 5e, BG3, Action economy really controls the battle. Since BG3 player action economy can be stunted...against multi attacking lvl5s, its a good idea to control the battle other ways.
OH and IVE NEVER SUCCEEDED a CONCENTRATION CHECK EVER IN BG3, but if you feel lucky there is also bless and bane.
