Ok, so you stated that you think of the ground weakness would help support the concept, and then you explained exactly why it conflicts so horribly with the concept. As you said, the ground weakness would allow a lot of Pokemon to score a solid hit on it, which is exactly why it is so incompatible with the concept. "This Pokemon is capable of being customized to counter virtually any specific Pokemon". That is the concept, not "This Pokemon is capable of being customized to counter virtually any specific Pokemon except for the huge amount of Pokemon that regularly carry a ground move". Keeping the ground weakness would make it extremely difficult if not impossible for this Pokemon to be customizable to counter Pokemon who regularly carry a powerful ground move, and therefore completely defies the concept.
Celebi does not exactly do what is called dying to anything SE, and it has 7 weaknesses.
Also, think about this: Ground is at the front end of the metagame. NOTHING THAT DOESN'T ALREADY RUN IT WILL TRY TO IN ORDER TO BEAT IT SPECIFICALLY. Flying and Psychic are decent types that much of OU can run viably, except the OU metagame has too few threats that are weak to them. Metagross and Jirachi can easily run Zen Headbutt to get rid of their counter, the only reason they don't is because they have difficulty with Infernape anyway and there really isn't much use BESIDES shredding the glass machinegun Ape. If this guy gets fighting, why exactly can't Jirachi just flinchhax CAP10 to death?
