My underrated players from this era (off the top of my head) is Jack Walker, Harry Cameron and Harry Westwick.
Players from the same era I would consider a bit overrated is Hod Stuart, Eddie Gerard and (to a certain extent) Sprague Cleghorn. Doesn't mean those players were bad or didn't make some difference for their teams though.
Walker and Westwick were the preeminent defensive conscience players in the 7 man game, outside of the offensive center position (rover or winger). Nighbor also brought this type of game to the center position (he kind of had to because the NHA abandoned the 7 man game well earlier than the PCHA, so there was no extra guy there to clean up behind you if you were going full throttle offense). McGee had Westwick and Bowie had Blair Russel.
Hod Stuart's value is a bit dubious to me. He hopped a lot of teams and when he finally won a Cup with the Wanderers he doesn't seem to have been a very decisive player. Let's just say this team won several Cups without him. I don't even know if he was a better player than his younger brother, to be honest. Or better than Moose Johnson.