Fritz leading the head to head 6-1 has already been mentioned in the OP. All 7 of those matches were on hard courts, and Tiafoe has only won 4 sets total out of the 18 they've played. Foe hasn't beaten Fritz in over 8 years.
Based on the things above, Fritz has to be a heavy favorite.
I think the only way Tiafoe wins this is if Fritz gets nervous and plays flat like he did a couple years ago when he choked his way to a US Open 1st round loss to Brandon Holt, or if Tiafoe plays the match of his life. If they both play their usual level, Fritz is just a better player in almost every aspect of the game.
(Throw all that out and I personally want Tiafoe to win. I just don't think it's going to happen.)