Yes, hardcourts are the main problem of course, but they are the vast majority of the tennis calendar, including two Slams. HC Slam matches featuring two of Nadal, Djokovic and Murray have become almost unwatchable, they will be pushatons since neither of them can hit through the other's defense.
Clay should be slow (maybe with a few midpaced tournaments), grass should be very fast, outdoor hardcourts should alternate between medium paced and fast but not too fast (maybe one or two slow HC tournaments), indoor tournaments should be fast. Something like this anyway
That way, you'd have to adapt in order to be a top player. We'd see more surface specialists of course, but you'd need to be able to adapt your game to different conditions to climb to the top of the rankings.
I honestly miss surface specialists (mostly grass-court specialists
) The point of different surfaces is to make the game different and that's part of the reason why Tennis is a great sport. But courts of the same speed just generally don't make it interesting.