So whilst I am still enjoying Act III despite the fact that it does feel incomplete (mostly for me in terms of the reactivity of certain companions e.g Halsin) I totally agree the martial/caster balance is totally lopsided.
Of course BG2 had insanely OP items e.g. the Robes of Vecna, so I'm happy that Larian went in that direction too, rather than using 5e's itemisation which is very bland.
For caster balance, my main three suggestions are the following - I think I might post a more fleshed out version of this post as a separate thread.
- Add a legendary (ideally in late Act II, early Act III), that allows you to maintain concentration on 2 spells at the same time. This is of course mega-powerful, but Chronurgy wizards can already (sort of) do this in tabletop - and I see this as one of the only ways of creating an item for casters that can be balanced against the martial items. I'd make the legendary a ring so it doesn't clash with other caster gear.
- Almost all the CC spells need a balance pass (see my extended post when its ready)
- Only arcane/divine casters can use arcane/divine scrolls. (Casters technically should roll a check if its higher level than what they can currently cast - but I'd ditch that here). Sadly I really don't see Larian ever doing this one as its quite contrary to their style of play, but I do think its needed personally.