Minus Nature Fire Blast usually 2HKOs Growth. 50 Base Special Defense doesn't quite cut it in comparison to Celebi's 100.
Swords Dance YacheChomp can be mean as well. Well, it won't 2HKO using Fire Fang (not counting Leftovers, anyways), but Stealth Rock and/or Sandstorm pretty much means Tangrowth is 2HKO'd while Chomp lives with Yache Berry. SD Outrage is pretty much a guaranteed 2HKO, but, in fairness, it's so on Celebi too. I don't think Outrage is quite standard on the SD set, but I've seen it used.
I think that a lack of fair recovery really hampers Tangrowth, here. While it's excellent at taking most Choice Chomps (obviously not Specs. =P), provided they don't pack Fire Blast, it can't quite keep coming in to repeat without some generous Leech Seeding.