50% of the player count are bots that do not cheat ... maybe.
I have been thinking about this: With the recent advancements in AI could you build a bot that pretends to be a human playing the game (with some intentional flaws in its gameplay -- so no aimbot for example)?
I would imagine player behavior -- like movement around obstacles -- in tf2 would be a valuable data mine to train AI further.
Way back when TF2 was new, Valve put out heatmaps showing how their analytics tracked where players died in each level along with a bunch of other metrics. If that kind of data was public (or a major server collected their own data), I wonder what level of bots we'd have today.
I miss the old days of playing against Foxbot in the original Team Fortress. It sucks that bots are only used by cheaters/drop farmers these days instead of as an official way to pad out lobbies, or to let you play matches entirely single player.