The game is changing as well ... using Caitlin Bickle as an example, she was a wing on her high school team, and when I was coaching at Campolindo, I had my tallest girl on the wing as well. There's no physical reason that a taller girl can't make three-pointers as efficiently as a smaller one, and more and more six-foot girls are interested in playing outside than in the paint.
Now a 6-4 or 6-5 girl (equivalent to 6-10 or 6-11 on the men's side) is pretty clearly going to be a post, but there are a lot of quality programs that really don't rely on posts to be successful. The way the game is played now, you can score without size, which means if you can neutralize size at the other end, you have a path to plenty of wins. And sometimes an active, strong, intelligent 6-1 woman can make it very hard on a less mobile 6-5 post. And then, at the other end, you can force the 6-5 post to either play man-to-man on the perimeter against that 6-1 woman, or she has to sag back into a zone. And if you have enough shooters, zones don't work that well.
Would any coach love to have a talented 6-4 post? Absolutely. But if not, shooters and long, active defenders can work too.