Honestly, I think my main beef with the fight is that the intended 'clever' way doesn't make much sense to me thematically. Firstly, while I am not an expert on the physiology of giant spiders, I expect with 8 fairly flexible legs it should be able to absorb falls pretty well and not take as much damage as it does. Secondly, it's a phase spider - it could simply phase/teleport while falling.
As for separating characters, that's obviously a good strat here. I just wish that the BG 3 'chain' group mechanics didn't make it so tedious by having to switch it off and on all the time.
