Jaheira I think should be hexed by a curse of the Absolute, and we see that happen, like where Thorm casts a spell at her. Something that knocks her down a peg, and this could explain why she's coming into the party at the level she is. Could work for anyone I guess to explain that going down. Or maybe the prism somehow does that? And we get a throwaway line there, something simple to keep it on target.
To be honest I tend to let things like that slide. Remember when you meet Jaheira and Khalid in BG1 they're supposed to have had adventures with Gorion a couple of decades earlier before he adopted the Bhaalspawn. So they should already be very experienced at that point, yet they're only the same level as you; a kid straight out of Candlekeep.
