So I actually agree with the OP.
Out of all the returning characters Jaheira is so damn well done.
Okay, on my 1st run I played basic Tav and didn't really take her much with me, only for her quest and to recruit Minsc, but she was likable.
On my 2nd, Dark Urge run my plan from the get-go was to get both Jaheira and Minsc asap just to drag them around together with my LI (Astarion). And oh my god, Jaheira is fantastic! Durge also brings all of the fantastic writing out of her as well! She's basically acting as the equivalent of Gorion to Gorion's ward. She's the mother figure Durge (if you keep on resisting Bhaal of course) never had! Beautiful relationship!
Minsc VA did a good job, but like OP said - took a little bit to get used to. Matt Mercer's version of Minsc seems a lot less... chaotically unhinged than Jim Cummings'. But still, aside from somehow getting Jim, I can't really imagine anyone else but Matt pulling this off.
Writing wise it's really hard to mess Minsc up as well, so there is that. BUTT KICKING FOR GOODNESS!
Now as to the other 2...
Viconia's entire redemption arc hinges on Gorion's ward romancing her. You didn't romance her? She remains a neutral evil Sharran, if somehow softened a little bit. And yes, i took her on my neutral aligned BG1/2 runs. If I decide to replay BG1/2 one of these days I should finally swallow my pride (just like I did with Morrigan's romance in DAO) and make a male Gorion's ward to actually experience the romance everyone raves about. Also, iirc if you played an elf Viconia would automatically reject your advances, no? She only accepted humans and half-elves in the originals iirc.
Anyway, as to Sarevok... I really cannot fathom why WotC insists on him being immortal and regressed back to worshiping daddy dearest... Sarevok's redemption arc was the best damn thing of ToB! You basically said everything there is to be said about how Sarevok's character got ruined!
Like damn, I remember crying like a little baby when Sarevok's ending slide rolled around and how he did his best to atone for his misdeeds by wandering around aimlessly, righting wrongs, conquering towns ruled by tyrants just to disappear after, the realization of who his true love had been all along - Tamoko (who died over the course of BG1), only to carry her remains to her homeland, properly bury her and disappear never to be seen again.
And to turn him into a monster who's into incest... I can't. I just can't!
But again, I don't know who's more to blame for these problems, WotC or Larian?