Patrick,
I think you are mixing two questions together. You say you are asking about the distance of the tee from the green, but then you switch the question to be about "universal challenge", where women, seniors, and top amateurs are all playing from different tees that don't present the same challenge to everyone.
I don't see how the amount of challenge could matter just by having the tee located further from green. In fact, I'd suggest that if you require the tee to be within a few paces of the previous green, the challenge would by necessity be REDUCED because the architect would be more constrained in his choice of green sites by the need for that green site to work as the starting point for the next hole.
Now at this point you are probably warming up the green ink to point out all the great classic courses where the tees are right next to the previous green, or were, and were made worse when the tees were pushed back to lengthen the holes. But I have to wonder how much better some of those courses could have been if the architect had freed from the requirement to keep the tees close due to the fact that all golfers walked from green to tee.
If we all drove around in carts that could do 100 mph even a quarter mile would not be an unreasonable travel distance. Maybe if Pine Valley was on more land Crump could have produced a course even greater by the greater flexibility that would have offered. I'm not advocating long trips from green to tee, I'm just saying that if travel time and land use wasn't an issue, I can't see how the challenge could be worse, and a good architect should be able to find better holes in the larger area and thus increase rather than dilute the challenge.
As to the second part of your question, you already know the answer. Yes, the need to make par was the driving force behind multiple tees. If women were willing to accept higher scores and more fairway wood layups/moveups per round, they could play from further back on many courses. But some challenges would be lost by the need to accomodate them -- pretty much any forced carry would be lost. Say goodbye to Merion's 18th, and many other classic tests, so relaxing this requirement would reduce the challenge in some cases.