Umm.. well those are both survival games, and Valheim is definitely also a survival game. Now Rust is a fast-paced survival game that caters itself to PvP while rewarding players who are willing to take risks. Valheim is definitely then more similar to Minecraft where you invest a lot into the equipment you carry around while decorating your home base to be your perfect dream home. PvP is so badly implemented in this game that it effectively doesn't exist. Also there's a penalty for dying so the game definitely favors a more cautious and thoroughly prepared approach.