I think that grading routes for an onsight attempt would make the most sense. So yes, after you have made the FA (lead), it is reasonable to imagine how much harder the moves would have been had you not had the beta. Best to then send a friend up for an onsight second ascent to test your grade, and adjust accordingly.
That system seems to work well for rap-bolted sport routes, but gear routes I think are a bit more complicated, and I really don't like the YDS for them, although it is obviously the norm around here. I think an ideal system would account for: the onsight difficulty of the climbing moves, the amount of pro, the "trickiness"/reliability of the pro (both of these factors contribute to the mental difficulty of the climb), and also perhaps objective dangers such as sharp edges and loose blocks. I guess the closest thing to this that exists would be the British grading system???
Another thing that I dislike about the YDS (for both sport and trad routes), is that it doesn't take into account how sustained the route is. So a 5.7 pitch with a single 5.10 move is graded the same as a pitch of sustained 5.10. Obviously one is more difficult to climb than the other, and it takes an attached route description to tell us this rather than it being decipherable from the route grade alone.
