Its actually not that hard to implement something like that. Its called sanity check , and it works on the networking model they use(which is the WORST btw).
Since the server has no authority in this game, they can implement a sanity check method , that runs on the client. Basically what it does is this function will check other players speed, cooldowns , ability usages ,etc, and if the cheater is doing some weird stuff, the sanity check function on the other non cheating players, will notice ,and take action accordingly.
There are some limitations here too, but still, it can help A LOT if they do it.