Well first of all, segwit doesnt affect the quadratic hashing attack vector because legacy non-segwit transactions are still valid even with segwit activated, so the attacker would just use non-segwit transactions for his attack. Flextrans (a bitcoin classic proposal) on the other hand could actually solve quadratic hashing.
Secondly, the Chinese miners overwhelmingly support segwit2x, including the 2mb HF that comes with it. If they are trying to keep asicboost (which has not been proven to actually being used), why would they support segwit2x instead of trying to force BU instead? Segwit2x includes....you guessed it....segwit...which disables covert asicboost.