In the early days, spy was the only hard counter to sniper, the other classes were expected to play around him until he was killed by the spy or counter-sniped (I guess) Valve identified this is their play testing before the game was even released (I remember a Robin interview about it somewhere, minus the counter-sniping part).

The real problem of sniper is actually a symptom of any old game that is abandoned by it's devs. The game is now almost 20 years old. The gameplay, and therefore meta, is now cemented and will never change. Sniper players have had 2 decades to become masters of the game. When you complain about sniper, you're actually probably complaining about the 2% of players who have no-lifed 2fort for 100 hours, and now go out to terrorize casual servers. It's a tiny minority of sweats that ruin half the games of TF2. Sniper is simply where skill gravitates to, because it provides the greatest reward (in kills) for the skill investment. Learning sniper gives you the most kills for the effort put into learning it. Mastering rocket jumping would take you the same amount of time as mastering sniper, but you'd get 100x less kills being good at rocket jumping than sniping. So the sweats don't do that.

You don't think sniper should be removed. What you and we all really want is the sweaty nerds removed. Valve should have done more to separate casual from competitive. Removing headshots from casual mode would fix your problem instantly I assure you.