I don't know that I quite agree with your view of history. Horowitz had a fabulous technique, but he made plenty of mistakes. I think there have always been supervirtuosos from Clementi onward, and there undoubtably always will be.What's more, we do still see major pianists who do not have major techniques: Mitsuko Uchida, Murray Perahia, to name a couple. But even they set themselves up to fail. I have said time and again in this forum that the problem is recordings. Check out Perahia's perfect recording of the Chopin etudes, I seriously doubt he can perform like this. It's tough when a musician can't compete with his own perfection.There is a huge difference between technique (e.g. Horowitz) and perfection (e.g. Pollini). Competitions and recordings have forced pianists to go for the latter. I do still think there is room for "imperfect" but highly interesting pianists, but agree the space is rapidly diminishing. What is pointless are the people who judge a technique by number of wrong notes. Barere's Islamey would probably be laughed out of a major competition today, technically awe-inspiring as it is.
Murray Perahia and Mitsuko Uchida have FABULOUS technique. Their playing is at the highest level.
It's probably all part of the evolution of music. If classical concert playing becomes too hidebound then it will die out. Human beings will always desire to be stimulated and moved by music. If classical concert playing ceases to do that then other forms of piano playing will emerge to take its place. One such direction could grow from the solo improvisation concerts of Jarrett and others like Jarrett. Piano music will continue to stir and move people and players will continue to take musical adventures and risks; it just may not be through interpretive concert playing any more, that's all.
What's more, we do still see major pianists who do not have major techniques: Mitsuko Uchida, Murray Perahia