I don't think they are "bad on the track" generally speaking. "pressure on the rails" does not compute. If I understand correctly the big issue FGLK had with them was there were too many places they could not go due to the long wheelbase. Inside the army base? Guaranteed derailment. Around the curve at Victor Insulators? Forget it! Phelps Supply? Not a good idea! 4 axle power is more versatile and flexible in the assignments it can work.
C628s had tri-mount trucks with an uneven axle spacing which made them rougher.
So far as I know there's just a few tight spots that are real issues, like the curve by the prison in Auburn. But as noted the six axle power isn't as flexible to use in tight spots on sidings and so forth. I would imagine the ramp down to the former PRR is tough too. Other than parts of the former LV none of it was ever a mainline.