If you're saying weighting can cause a big disturbance from a minor shift in hashing, that phenomenon seems much less likely to occur with 4 algos instead of 2 if weighted properly.

It's obviously also much more cartel proof.

People like Gmaxwell seem to claim that a group like KNCminer would create ASICs for all four chains.

I don't really see groups like that monopolizing all four chains into eternity, especially if each algo is radically different from one another.