Pretty much yes. The only one I'm not 100% on (besides the scout skin, since that was after I stopped playing) is the engineer prosthetic. I feel like that weapon came out a while after TF2 was made (but I can't check that right now so don't take my word for it).
Jarate and heavy x medic were after release too afaik.
Heavy x medic was kinda obvious, but iirc valve didn't start dropping stronger hints until the past few years. Dunno if they've straight-up confirmed it yet or not; it's also been a while since I last played.
Jarate was part of the sniper update, which I thought came after release (because iirc there weren't any alternate items in the original release).
99% sure Jarate was in the first big alt weapon patch, because it's the last patch I enjoyed playing lol. Bow, Sandvich, Bonk, etc. came out at the same time.
Outside of the game, maybe? I've played a ton of TF2 but never got involved in the outside memeing or story. In-game there's nothing obvious about any of them except Soldier sounds thick-as-pig-shit and Demo-man being black.
One of the Engineer's unlockable weapons is the Gunslinger which is a prosthetic hand. It also is (or was) commonly regarded as OP since it replaced the turret with a fast self-building mini-turret that was a pain to keep destroyed (Engie would toss out another one).
Ok still is. Wasn’t saying it isn’t currently but all these decisions were made like 15+ years ago. Hence “ahead of its time.” The implication is many of these decisions still hold up very well to scrutiny.