Parker biggest problem is he has decent hand speed but is far to passive. If he had the aggression that Ruiz had then he could have had a chance with AJ instead he lost a dull points decision. He's won some fairly average fights since but has he got any kind of draw to drag a Fury or Usyk into a fight - probably not. Parker V Whyte could be interesting but he would need to up his work rate to stand a chance of a win.
Only thing I can see diminished is his punch resistance and stamina. It's amazing how far he got with a big punch, his footwork is non existent. he throws punches off balance , and his defense relies on the fear of his power.
Wilder is still a formidable opponent with that one shot power for any current Heavyweight not named Fury. I’ve mentioned it before but there are some good fights out there still for Wilder to be involved in .
Ruiz Jr went into the eye of the storm. Parker was just happy to go 12 and not get knocked down. His old team marketed him having never being down heavily in the lead up to that fight. I believe they prepared him to be happy to survive.