By the contract, you couldn’t say anything detrimental about the game, so such a statement would still be forbidden. Whether such a vague limitation on what a content creator can say would hold up in court is a different thing.
No launchers at all? They do help to organize the game library, synchronize saves across devices, enable achievements and friend lists, make it possible to share game libraries, install all your games from a single place, have a shop to discover new games. Steam even provides basic APIs for games to enable multiplayer. Many of these things could be baked into the game, though that would be extra work some devs might not do.
One centralised launcher? Such a monopoly might lead to problems such as higher prices / less money for game devs (especially the good indie studios that don’t have negotiation power), less innovation around that launcher and less effort towards a good experience with few bugs etc.