Yeah, I'd say you're off base on this one.
Coaches make a world of difference. Communication, motivation of individual players, ability to adjust in-game and between games, attentions to detail with the team and certain players and maintaining respect and authority over the years vary wildly from coach to coach. Even at the NHL level. You need look no further than the turnaround this team had when Jacques Martin came onboard.
If anything I'd say captain makes not much difference in many, but not all, cases. You don't need Mark Messier as captain if your core group of players are hardworking and play for each other. A young team just starting out, however, likely benefits greatly from a strong veteran captain.