I think the wear and tear of 130 games a year catching would diminish his ability to he as productive as a hitter.
How many guys were able to catch regularly and remain significant middle of the order hitters? Piazza. Posada. Javy Lopez. Pudge Rodriguez.
Bench, Fisk, Campanella were way before my time.
Most guys are able to catch regularly and remain at whatever the level of hitter that they are for quite some time. If someone is a great hitter like the guys you mention, they can remain so for many years. If they are a average hitter like a much larger group of catchers throughout history, they remain so. If they are below average, like most catchers, they stay there. There simply are way fewer guys qualified to catch than there are qualified to do anything else, so you see fewer studs there. Like if only one in 15 hitters in MLB ever existed at all, you'd see far fewer great hitters than we have.
I think you'd have a case for career longevity being at risk as catcher (though not as extreme as I think the general belief is of the falloff for catchers), but I don't think overall or peak ability is really at jeopardy if he catches vice plays first, aside from the obvious need for more rest and how that will limit non-rate accrual.