how do the pros use Pianoteq Pro?

The old adage: "if it ain't broke, don't fix it" applies here, for me at least. It's not because all that power is available that you have to use all the features on all the pianos. It's easy to get lost in editing...and even forget why and where you started in the first place! Large changes in too many parameters at the same time tend to denature the sound, to make it worst...
I use the Pro features to fix something that bothers me. Usually, it applies to a small number of notes. If a few notes ring too much, or don't pop enough, I try one parameter at a time (typically Hammer hardness, Cutoff, impedance, and do small adjustments. I have also created a few Morphed pianos (without spending too much time on it) and I use them often. The power of Pro is that it allows  individual note or different note ranges to be edited separately. That is the main thing.

I know different users might try more extreme things, on tuning, string length, etc...but I prefer to spend as much time as possible PLAYING and RECORDING. But if something in the sound bothers me, the tools to fix it are there in Pro, and it is well worth the investment. However, recent versions of Pianoteq are so improved, that I find myself playing the basic factory presets more and more. And I can tell you, it is only getting better!

Yes, some excellent advice in the posts above. The note-edit feature is a great tool for subtle tweaks, and it's best to go in cautiously if you're aiming for a realistic piano sound. But then, if you're into sound design, there's no reason why you can't go crazy and mangle your pianos out of all recognition! I tend to do both. If I want a classical piano sound, I make only minimal changes to the default preset. But I also enjoy experimenting with weird tunings and fx, using Pianoteq a bit like a synth. There are the morphing and layering features as well, so you can create hybrid instruments. The possibilities are endless.

Seems to me if you want realism, you're better off just accepting what is thrown at you from Pianoteq, with minor changes for room acoustics.
But even an acoustic would exhibit those, and most would accept such.
The main feature pros use is their advanced level of playing.
They'd sound good on anything.