The problem I have with the amount of "expected" time stated instead of length is the amount of time will inevitably vary for every party. It seems to me that someone's Grade II can be easily someone else's Grade I and vice versa. That is why I prefer Jerry's approach of specifying the length of the route, and presumably a description of the pitches and the terrain involved.
Yes it is a problem. and the solution is not easy. What is more dangerous? someone who think that he can climb a route of 900 feet Before dark or some one who know that he need at least seven hours to do the climb. Of course, I can climb white horse slab in thre and a half hours with most climber, but the idea is what is more dangerous? In Webster, we have the number of pitch. If you climbed very often on remote area, you will know that it is not the length of the pitch that took times, it is to built the anchor, and rope manipulation at the belay, drinking and eating.
For me, time is very use full because if you climb half the route in three hours and the route is rate four hours...you are two hours to slow: you climb over your helmet. On the other side, if you take one hours for half of the route, there is a good chance that the route is too easy. So, some one who climb the classic route of an area and who has a good estimate of his time of climbing can, with the difficulty scale, decide a route where he will enjoy the day safely, even if it is not a classic.
Whit the length of the route, it is not possible. because you know that you climb half of a route, that's all.
What is the problem with the time, it is that it is the time for the average party to climb a route. That notion of average party have to be specify to understand what is both an average climber and us as a climber. If I am faster than an average climber, What that means? The problem is in the definition of it.