Procedural generation is not gameplay. Procedural generation makes your already fun game more interesting via more variety.

If you don’t already have a fun game, then pro gen won’t make it any more fun than it already is. It turns a fun 1-hour game into a much longer fun game.

If every single Minecraft player loaded into only a single Minecraft world, it would still be as fun as it is. Would No Man’s Sky really be that much different if it just shipped with a handful of pre-defined planets? It might have less replay value but the gameplay wouldn’t be any different.

Good proc gen changes things in your game such that the player is given interesting reasons to make different choices each time they play.