It depends on the kinds of inputs the fighting games you play require, as well as the speed with which you gotta do those inputs. Also I'm prolly in the thousands of hours vicinity lol. I play guilty gear, under night in birth, blazblue and more recently granblue versus, outside of granblue all the other ones require a ton of inputs, especially the chars I play (Sin and Answer in Xrd/ Seth in uni/Bang in BB).
Especially things like microdashing and instant airdashing which require precise and speedy inputs and which you do dozens of times per match at a high level take a toll, as well as blocking low. One of my pads just doesn't register the down forward input at all any more and the other just freaks out entirely and is unusable. Thankfully the one that just doesn't register downforward still mostly works and since it has the Ragnarok sticker from valkyria chronicles 4 on it and it'd be a waste to not use it on other stuff. I still play other non-fighters with it, while I am on ds4 #3 for fighters. So far so good with it. (this is in a period of about 3.5 years, contrasting it with the ps3, I had the same ds3 pad for about 6 years and then I got another one when that finally gave out which still works, though the ps4 games don't allow it to work so I can't use it for ps4 games, and I actually played even more back then than I do now cause I was learning the genre)
Oh and my left thumb does have a decent guitarist callus that's been there permanently for years, though it's not like I press the buttons hard, it's just the friction from the speed that causes it. My right thumb has no place in fighting games, I use the claw technique (right hand using index/middle finger to hit face buttons).