1. stop thinking so much
2. mge is a way to shoot at people so you get better at shooting at people simple as that
3. most of the time people in mge servers whining at your playstyle are wrong
4. im also wrong a lot so take everything with a grain of salt
5. not sure what you mean by problematic peripherals but yeah if you have a cruddy mouse and a 60hz monitor you are going to have a bad time its still possible but it takes a lot more work I played multiple seasons with fps drops to under 60 and its the sadzone
2500 hours is a long time (maybe not compared to random dudes who have 5k+ but still) and I know not seeing improvement sucks I literally quit every single thing I do in life unless I feel improvement but if you enjoy tf2 try to stick with it because there WILL be a point where you are better than you were before
IMO if you arent having fun you generally wont be in a good mindset for improving
example being if you find yourself thinking about random negative stuff while mgeing or scrimming its just going to taint your practice time and sap your energy/fun
for me it was constantly thinking about what my opponents thought of me like id maybe randomly run away from someone and pistol them from far away or spam double jump a few times in a row and id just think "man does this guy think im a pussy now" "omg hes going to shit talk me or something"
try to just focus on your aim or movement or both and developing good habits but if its too crazy to think about and you are worried about etiquette and everything just reset to ground 0 and remind yourself that mge is just a place to shoot dudes and everything is fine
if you stick with it you will see improvement I promise its just a matter of time everyone goes through patches where they see less improvement or more improvement how good you become is based on how much you love and commit to the game example b4nny he has liked the game the most and for the longest amount of time so hes the best at it
god damn sorry for the wall but goodluck dude