See that gap in the data...that's when I was there. The gap is when Sunday's 1500 spike on Bailey made it to Waterton. There's a similar gap in the data for the "below strontia" gage.
Your point about it not being Class V because of the reservoir is fair, but I'd liken it to Tunnel falls on Gore. I'll run Tunnel (in part due to the big friendly pool of ego collection), but I sure as shit was not going to run what I was looking at in Waterton. To be fair, I've been known to walk Tunnel, but that's just because I'm an enormous pussy.
I've paddled Waterton in the high teens and would say, at that level, it's pretty straight forward and super high quality. Maybe not an "easy III," but for sure in that III/easy IV sort of range.