There comes a time when a pokemon so easy to use can completely change the metagame at a whim and the masses don't want it banned because it's the only thing they'll use to check a variety of threats. Shanderaa is that pokemon, it will be the pokemon you see on every single team because it's so easy to use. It makes clicking Bullet Punch look like rocket science. It will be far worse than Garchomp, because Shanderaa will eliminate the use of Choiced attacks that can't also OHKO it. Got a Starmie weakness? Scarf Shanderaa on revenge! Got a problem with Jirachi? Sub CM! Skarmory got you down? Any variety will work! You don't even need to use it properly to get a single kill every time since you can just throw it out on Revenge. Almost every pokemon that can be OHKOed by Choice Scarf Shanderaa has reason to run Shed Shell. Who cares if TTar revenge kills you, because at the end of the day this pokemon has done its job.
I personally think the exact same thing could be said about Gen IV Garchomp. Not to a bigger extent, not to a lesser.
Anyway, I see your poin't, which is exactly why I'm hoping for a Shadow Tag Clause. Think about it. Ban Shadow Tag and we've got an amazing, NOT broken pokemon. As I stated earlier, Flash Fire Shandy is a less defensive, more offensive Heatran. Trades the shitton of resistances for much more Sp Attack. Flash Fire Shandy seems like a legit OU pokémon to me. I can't wait to test her in Wi-Fi.