Please do'nt forget that you compare old tires with new tires.
I am quite sure, when PR4s are old and probably square-edged, new Scorpion Trails will feel much better than the old Michelins.
Which does not mean that PR4 is not an excellent tire. But the comparison is not "objective" because the Pirellis you have old and used in mind, the PR4s new and fresh.
I had this feeling all the time when i changed from old to new tires, even between the same brand and model.
But you are right, tires can transform a bike completly.
I use Pirelli Angel GT at time and for trackday use i switched to used Supercorsa SP. The bike handled completly different, more handy.
They have different contour, additional, you wear them on different areas and angles, so, after track use the tire feels different to the time before. The same is with a tire at roaduse.
When i switched back to my used Angel GT now, bike felt completly different the first kilometers until i got used to it again.
