Valve doesn't test enough or they wouldn't have to nerf their own updates (ie pyro).
The stun time is way too long. Anyone thats not buffed or a heavy is pretty much dead if he gets sandmaned.
Again I have to disagree, on a one and one situation if im a solider, medic, or a scout my self, I end either killing the scout or getting away. And in most cases I have back up, and yes its true not all hevies have dedicated medics, or a medic at all near by, and I don't know why they don't, or atleast I dont know why they don't and are out in the open with out any other class backing them up. I've always felt that TF2 is a team game and besides snipers and spies, I dont know why anyone would be anywhere completely alone. But even with out any of the new weapons, which I do not own, since I only have eight achivments and have not/will not go to an achivment server or farm them, can usally take a heavy with 3-4 rounds from the normal scatter gun running circules around the guy.
As for valve testing, im sure they test alot with a small group of people and see no problem with it but when you give thosands of people the same weapons, new ideas and concepts start to pop up so you need to change acordingly, and didn't they only change the 50+ hp from the backburner or was there more I don't remeber?
I could be wrong who knows I don't work there. But I dont feel anything needs a nerf yet, I find baseballs are easy to avoid as long as they don't ambush you with them, and so far I havnt really played scout that much, im usally a medic/heavy/soldier or sniper. I think thats what scouts should do, is ambush, and hit and run tactics, and now they have become a more interesting class with interesting abilties, before this they were usless, only used to get kills and brag basicly, like weak characters created for fighting characters, only for bragging rights. Now Valve has attempted to make them more useful to the team, by being about to counter ubers and distract or pass sentires and so on and so on. I think alot of the hate for the sandman comes to people who don't work on a team, or atleast that's what ive seen on blackmesa, when spawn camping is the thing to do in that map. Your usally only seeing 2 guys useing uber at a spawn, while in maps were the team is working together an uber is used to push everyone, not 2 guys, so if your target gets stunned, quickly grab the next useful class next to you, to push. Or alteast thats how I do it.
But I am no expert or anything, just my 2 cents.