Thanks both for your replies. Perhaps I’ve been a bit too prescriptive. I know this question is complex (and I’ve read the recent series of articles on strength), but that’s why I think it’s worth asking.
I tend to think of the necessary skills on an alpine route (as far as the climbing is concerned) as physical fitness, movement skills (climbing technique), technical skills (rope work, placing gear, etc.), and mental stamina/head game. I know success depends on the whole package, as implied by the idea that M5 with no pro is different from bolted M7. I also want to avoid a false dichotomy. There is a middle ground between sport bolted M-climbing on the steeps and runout, high consequence, big alpine routes. This could be gear protected M-climbing with consequence, but without the commitment of a huge approach, a bunch of less technical terrain before/after, a bivy, complex descent, etc.
This leads me to two thoughts:
1) For this sort of thing to be an “endurance sport,” it must first be an endurance activity, which implies to me that there should be no question about whether you can actually do the move, but rather how many times you can do the move. In that case, it seems the answer is that the point at which you’re ready for a committing route is the point at which the movement is so facile that it is purely endurance. However, this likely precludes a lot of difficult climbs that are closer to the margins, where it’s a bit more of a fight and not necessarily given that the move will definitely go.
2) I might just be looking for a personal benchmark or confidence heuristic. For example, Scott Semple, before you headed up DTCB with Raphael Slawinski, how hard were you climbing? How did you know you were ready for that endeavor? Or, how hard were Steve House and Marko Prezlj climbing to feel confident heading up the West Face of Cayesh? Surely these things are closer to the limit and with smaller margins than pure endurance, so how do you decide what the margin is? (Please correct me if I’m wrong–it’s certainly possible these really were simply endurance exercises and the skill of the climbers is far beyond what I’m giving them credit for.) To be clear, I certainly see the value in working up on easier routes, but I’m also trying to set some concrete goals on the movement and fitness side of things (without neglecting the mental game and technical skills as appropriate).