>>369490081) Bullet Punch isn't in the move data in this game, so we don't know if Melmetal will be able to learn it in Gen VIII.
2) Melmetal still has Thunder Punch, Ice Punch, Double Iron Bash, and Earthquake. That shit alone will make it RU. PU is reserved strictly for the shittiest shitmons. A bulky Steel tank with high attack, defense, and HP isn't PU.
3) It doesn't even matter until we get to Gen VIII since Smogon doesn't lump unofficial shit in to their metagames. (Melmetal and Meltan are exclusive to LGPE and GO, so they can't be used in a USUM metagame.)