We never claimed Quark is bad for second-preimage resistance. It's pretty good. We claim Quark is no better for collisions than BLAKE-512, and we have proposed an alternative solution that does not rely solely on BLAKE-512.
And that's wrong and easy to prove.
In Heavycoin if one of the 4 cryptographic hashes is completely broken, then you lose 64 bits out of 256 bits. In Bitcoin if SHA-256 is completely broken, then you lose 256 bits. Both scenarios are unlikely, but in one of them you lose fewer bits.
If in Quark one of the 4 cryptographic hashes is broken, you lose - NOTHING!
I am going to provide you an easy to brake hashing function. Craphash(H) = ~H. Simply flip all bits. So, and now you claim that CrapHash(Keccak-512(Skein-512(Blake-512(X)))) or Blake-512(Skein-512(Keccac-512(CrapHash(X)))) is broken? Sorry, but that's ridiculous.