Please correct me if i'm wrong, but isn't Quark only as strong as the weakest of its hashing functions ?
No, the hashing functions are applied one after the other.
The result of the first hash becomes the input of the second hash, the result of the second hash becomes the input of the third hash and so forth.
So it's more like the layers of onion skin, and NOT like a chain (with a weakest link)
so, in pseudo code:
hash9(hash8(hash7(hash6(hash5(hash4(hash3(hash2(hash1(...)))))))))
(now correct me if I am wrong)