[romland]

There are many reasons why a server must "over-share" in a game:

- Bob and Alice have different latencies and are walking toward eachother, lowest latency will have a huge advantage (there are of course mitigations for this in games, but it _does_ involve the client doing some of that work)

- There's rendering: Alice opens a door, behind that door was Bob but he will only plop into view later for Alice; which makes for a rather ugly and awkward experience in a game

- in the same vein, in a fog of war, people can very quickly change their line of sight -- server will want to share this information with clients before-hand

- As for data that is _always_ there: take 'aim-bots' which just harvest data from targets in your view and well, target them in the best order

Making a competitive multiplayer game is hard.

All that said, cheating is harder in streamed games. Client will send controller data, servers only send video streams; in this scenario you'd still have the aim-bot problem, but a lot of other cheats go away.