I'll start by saying that I am fully aware that this question might seem subjective at first, but I'll try and provide a specific test case scenario for it to be a clear question about validating the data received from 2 multiplayer game clients.
After a turret is placed, a bunch of enemies are released from both sides and move in a straight line towards the other side.
As soon as an enemy reaches turret range, we can assume that it is destroyed in 1-5 shots. If it takes more than that, the enemy safely passes to the other side. Now, my problem lies in the fact that usually I would do all the validation server-side, but it becomes increasingly difficult to do, because I would need to simulate every step of the game.
Instead, I would like to depend on the event data (enemy destroyed/enemy gets safe passage) received from both clients.
The main question then is this: