I can certainly see how Witten's contract vs. performance could be viewed as him not playing up to his contract. Looking at it from a simple black and white perspective (Pay vs. Production), it looks out of whack. However, football teams deal in many shades of gray and things aren't always clear cut. What Witten means to this franchise goes well beyond his on-field production... and I'm not talking about sentimental aspects either. I mean the leadership and work ethic that he brings to the team. The stability and the precision. The pressure he puts on defenses to just keep an eye on him helps those around him and his run blocking is still near the top of the league for TE's.
There are a ton of things that he does that helps Dallas win games and none of them have anything to do with legacy.
Can he stretch a defense down the seam much? No. Can he get yards after the catch? Hell no. But there are so many things that he does that helps the W/L column... in the locker room. At practice. And still on the field.
Now, would I like to see what an O.J. Howard could do with Dak and Elliott? Oh, hell yeah. The passing game would be harder to stop with that kind of athleticism at TE. However, his run blocking wouldn't be as good as Witten's. His leadership would be a tiny fraction of what Jason brings to the huddle, and his reliability would be much less for Dak at least for a couple of seasons.
Bottom line is, I would love an athletic TE too but fans don't see everything that Witten brings to the table and his significant contributions that can't be quantified are all too often overlooked or forgotten about entirely.
And I consider you to be a pretty well informed fan verdict, so I'm not putting down anything you said... just giving my perspective on this subject.
As for Dez... I'm too sleepy to get into that one. Maybe another day, lol.