Sadly, blocking isn't as "flashy" as receptions and yards.
So, I guess it comes down to how you view it. Some TEs are such exceptional receivers that you can overlook their average blocking. But if you put an emphasis on a TE needing to be good/great at every job that comes with the TE position, there really isn't many TEs better than Witten throughout NFL history.
I think Witten has fit perfectly with our schemes over the years. When we went to a more pass-happy style offense, Witten had 6 straight seasons where he averaged 900-1,000 yards. Now that we have moved to a run-first/balanced style offense, you might as well consider him another offensive lineman out there.
Either way, he's a future HOF no matter where he's placed on lists.