Dynaheir? Don't remember anyone talking about her, people ususally arranged "accidents" that separated her from Minsc so you can have free slot for Edwin...
Sparkle & Myles - good for not-minmaxers looking for a variety and challenge (by additional burdens)
Dynaheir's not useless, exactly, since sorcerer can be a powerful role.
But she tighten the tactical possibility. What if we dont want to use sorcerer?
Plus, she's an ugly one~ This one actually a valid reason why people like me dropped her into a deadly situation, 9/10 runs. If her character is, I dunno, pretty/sexy, and better avatar graphic... that ratio would be only 5/10 (because forced to use sorcerer still rankle).
Miria in Fallout 2, now, is useless. Most people would keep her only for the divorce event. Later on there's a mod that make Miria level up and not so useless anymore, but that's twenty years after F2 release~
Myron is not useless because he's the one where we can do the chems crafting: stim, super stim. It's a bloody challenge keeping him alive, but I dont consider that genius boy to be useless, considering super stim has widespread application for Chosen One. Without him that application fall right down to one or twice per game, with him it's as much as you can gather raw ingredient to make supers.