Underrated Characters?

Veers, Fulcrum, Talzin, Sabine, Oppress, RT and Old Ben all have a place in teams that can be competitive, or in teams that are good in Raids/TB.

Veers - Troopers
RT - zFinn
Fulcrum - alternate meta DPS
Old Ben - decent arena tank for those without GK/Chaze
Sabine - Raids and Phoenix DPS
Oppress - DS Sith teams, Solo P3 Tank
Talzin - could be new meta, certainly interesting skills

Of those, the only I'd say are truly "underrated" are probably Fulcrum and Old Ben as they are usually overlooked in place of Thrawn/DN/Leia in a meta team, or GK/Chaze.

The rest on your list.... Are more "garbage" than "underrated"