Everyone plays the game for their own reason. For one person to say "it'll screw up the competitive scene" if there's many unlockables is just as equivalent for a single player, completion seeking player to say "screw the competitive scene, we want more focus on our single player experience". There's no cop out for the latter for wanting replayability with unlockables, that's just how they play the game, they want objectives to complete, similarly how competitive players play to want to be the best. This is what makes MK more unique out of all the fighters because it caters effectively to both audiences.
This is why I propose they should give the player the option to make a one time permanent decision once you start the game for the first time. You either choose A. Competitive Experience, or B. Story Experience. Once chosen, you can't go back unless you delete save game data, so that way, you're compelled to stick to that one experience.