Wrong. Correct statement would be: It is impossible to prevent cheating without dedicated servers.
So, if the game developer decided to create multiplayer game based on p2p architecture, then there are ultimately only two options:
- this game developer knowingly / intentionally planned just to ignore cheating in his game completely, from the very beginning of development
OR
- this game developer is the most incompetent one in the area of multiplayer / network technologies in the world
Well, there is third option actually, but it's the worst one - developer does have competencies, and planned to fight cheaters. But he is too greedy to maintain dedicated matchmaking servers.
With dedicated servers, it is possible to make cheating impossible, though still only small number of games achieved this. As a live example - Eve Online. Cheats are impossible. There was only a dozen of not-critical exploits during the 16 years of game life, and even they were not cheats, but really just exploits - no hacks, just flaws in game mechanics which allowed for example "too easy" isk earnings, similarly to, for example, passenger sightseeing missions with too high payouts on start being registered as Explorer rank progressions. And all these exploits were fixed very quickly, while all earning made through them were fully reverted back.
Without dedicated servers it's even theoretically impossible to prevent cheating, and even just detect it reliably, without relying on player's screenshot/video reports (which, in turn, sounds like stone age thing).