A simple solution to combat all the cheating!

[KageTokage]

But how do you even tell that people are cheating/using mods?

Unless this cheating is blatantly breaking things like floating where you should not or running ahead before the match starts. Otherwise... only if they are telling you about that out loud.

Bots follow an extremely stiff pattern of movement/actions with little to no deviation.

The most common type of cheating in PvP is automatic skill triggers to secure kills or deny actions from the opposing team, and as with the bots, it happens with an unnatural level of speed and consistency that becomes pretty obvious when the same player keeps CCing you every time you try to LB or some such.