Bulk doesn't mean much when you have one of the worst defensive typings in game.
I understand that you think Zygarde is underwhelming compared to Garchomp, but that doesn't mean Zygarde suddenly has "one of the worst defensive typings in the game". That's a pretty fucking bold statement, and it definitely does not hold any weight whatsoever for a Dragon/Ground-type. Lets just break down Dragon/Ground defensively:
Weaknesses:
4x weak to Ice
2x weak to Dragon
2x weak to Fairy
Resistances:
Immune to Electric
Resistant to Rock
Resistant to Fire
Resistant to Poison
So while the typing isn't incredible defensively, it has two very good resistances in Fire and Rock and a decent resistance in Electric. In terms of weaknesses, it's very weak to Ice, and weak to Dragon and Fairy. I doubt Fairy-types will be super relevant considering the ones that have been revealed so far (Azumarill is the only one I can confidently say will be great), but anyways, that clearly isn't a horrible defensive type. Sure it's nothing amazing, but I don't see how it's half bad, nevermind "one of the worst defensive typings in the game"?
You're clearly exaggerating here because you have some sort of unfathomable and unreasonable vendetta against Zygarde (as evident by your posts in this thread). It's really not half bad. That physical bulk is fantastic, it has a very nice offensive typing, and it has two great boosting moves in Dragon Dance and Coil. It does faces some competition from Garchomp, but Garchomp doesn't have Dragon Dance (which is pretty much everyone's move wish-list for Garchomp) and Coil, which definitely gives Zygarde a niche over Garchomp.
Sure you can list every flaw (it doesn't have much) that Zygarde has... and nitpick every argument for Zygarde being a good Pokemon, but the fact of the matter is every Pokemon has some sort of flaw, however some have a lot of attributes that redeem it from its flaws, like Zygarde has.