most of the stress comes from I have to imagine. I have a buddy who's a former MLB pitcher, I'll ask next time we chat

I don’t know how catchers last so long!

They throw a lot, but they squat a couple hundred times a game.

The likes of Yogi Berra and Johnny Bench have had to learn new positions because of their knees.
The few I can think of that tasted most of a career at catcher were Carlton Fisk, Ivan Rodriguez and currently Yadier Molina. And I am probably wrong about them.

Most arm troubles comes from the different action placed on the ball by the pitcher, and most especially, throwing from a mound.

The mound is an elbow killer.

Ex-pitcher here.

college softball help?

The action and force placed on the arm from moving from an elevated position is quite unnatural. That is one reason, as you noted, softball pitchers do not have the same problems and can pitch on consecutive days.

One thing I’ve noticed is classic drop and drive pitchers like Seaver, Ryan, and Clemens seem to have fewer arm problems. If you look at their motions their left knees are practically touching the ground when they release the ball. That seems to leave their arms on a flatter trajectory relative to mound height which might lead to less arm strain. Just my thoughts.

Catchers don't throw curves.

-- Mal