I think you're better off if he can still catch. You just have to accept that you are paying all-star money for a good starter and nothing more. No different than Arrieta this year, or, quite possibly, Cutch next year.
It's not like there aren't tons of 34+ catchers out there. Yadi is 37 years old and making $20 million for 1.3 WAR and 108 starts. Chooch was 3.1 WAR at 35 and 1.5 at 37 (but bad at 36). Brian McCann started to shift from starter to back-up at 33/34 while still making $17 million (and is now done at 35).
If JT is as good as hyped/believed, and as important to the Phillies as they seem to think, 34 is not an issue and giving him the 6-7 years is something they will still have to entertain, if they think other teams might come to play in free agency. He is probably still a better, and less easily replaced, catcher at 33 and 34 than at any other position.
DH should be an interesting variable though.