This is one of those things where Valve actually actively sucks and is actively ignoring a growing problem because the old game just isn't profitable anymore.
Expect this to get zero interest or time spent on it from Valve because they're knee-deep in trying to release a Hero Shooter (rolls eyes).
I have a lot of respect for Valve, but situations like this really need to make people step back and question how much Valve care about the community that uses the Steam service, or do they really care more about how much money they make?
The fact that they keep creating micro-transactions for a game that's been completely taken over by bots says "They don't give a shit, they just want the money."
Thanks for coming to my TED Talk. Let's not let Valve get away with shit just because they're "good guys" compared to other businesses.
Anti-consumer is anti-consumer is anti-consumer. Valve doesn't get a pass for being Valve.
EDIT: To be clear, I understand that they aren't required to keep supporting a nearly-two-decade-old game, but letting it become a place where outright abuse happens is a different story. If you can't control the abuse and you don't want to do anything about it: do the thing nobody will like but will solve the problem: kill the damn game already if you don't want to support it. That's what I expect to happen before they face this issue, they'll shut down official servers and make the game unavailable before they try to solve the bot problem for a game so old. Valve has made it clear for years that they don't listen to or give a flying fuck about the TF2 community.