So the change in the quality, etc of the voice and how he is flat makes fans think his voice is damage?
Then yes sure.
Partly to do with aging too definitely.

Jon hasn't really used twang at all after the BWC tour which lead to him sounding pretty different since 2013. Twang makes you sound quacky or like a duck or something. Whenever Jon used twang he used an excessive amount of it.

He is very lucky to not have or had any nodules, polyps, etc. Loss or problems with falsetto/head voice is one of the absolutely first signs of vocal trouble/problems before anything else comes.

I think Jon only TRULY had vocal damage/strain during Slippery and Bounce.
I think April 1993 was mostly strain rather than damage which lead to some vocal trouble, but if he had continued singing like in April 93 during the whole KTF/Sleep tour it would eventually/definitely have turned into damage.

95/96 was probably a "balanced" combination of both.

Jon's correct technique 2008 - 13 was at times excessive, bad or just good.

Jon's voice has physically lowered and deepened between 2014 - 2018 though. I think his whole range has proportionally decreased 1 half step or maybe even a whole step since 2013 - 14.
His voice has become even older, manlier than before which is what I mean by deeper.

It's a very good thing that we have a thread like this now instead of always making a new thread of the same subject.