Subban wasn't going to be the backup goaltender this season anyway, to be honest. Maybe not even next year, or the year after that. I'm not sure I understand what the big frustration is here. Was it a waste of value? Sure, if you contend that Subban shouldn't have been drafted in the first round to BEGIN with.
It's a disappointment, but all things considered, with the strength of the team going forward, there's no reason that a trade for a quality backup goalie - or even a free agent acquisition down the road - couldn't be had. Besides that, K (Can't spell his name right and i'm not even gonna try right now) wasn't THAT bad last season. His first few games were atrocious, but they WERE under Claude. I doubt Subban would've played any better at the time. K played better under Cassidy though, so you gotta hope that this whole little "waste of value" isn't going to be anything significant down the road.
If Zane doesn't pan out in a year or so, then I'd be concerned.