Okay, this is silly . . .
Nothing EVER deals real damage to Tarrasque, under ANY circumstance, right? He is beaten by being nailed for Max HP +30 subdual damage (for those of us not using the standard Tarrasque), or 870 in most cases, right? You have to use Wish or Miracle at that point to kill it, right?
What the fark is the point of that? You'd get the SAME FARKING RESULTS from changing it to Fast Healing 40 and getting rid of that subdual damage crap, allowing everything to hit him for normal damage!
So what is the point? It makes no sense . . .