SSTO's are just fine on reentry with a couple tweaks. My new procedure starting with a circular 100km orbit is to burn to a Pe anywhere between 20 and 45 km. Set the SAS to Radial and rotate to make sure you're belly is facing prograde. The magic AoA seems to be 45 degrees. As long as I'm above that, I can reenter without any part breaking 400 degrees. Its fun, you can bounce the AoA down to 40 degrees and watch the nose and wings shoot up over 1000 degrees instantly. My planes go subsonic at 25km altitude and its a nice relaxing dive and flair down to the KSC. If you add a fair amount of wing surface and some RCS in the nose and tail to hold the AoA, you're golden.
As far as going super fast down low, the SR-71 had a top speed a little under 1000m/s at 24km altitude. Even the X-15 was 2000 m/s at 30km altitude. You have a point that you can't really do that anymore at that altitude, but in exchange, Squad has given us a wonderful airbrake zone between 30km and 45km that can decelerate anything as long as you keep the AoA up.