Also, if a large pool, or more, were to switch over to mine the BCH blockchain, the difficulty would adjust in such a way that it would make it very unprofitable to mine it over BTC blockchain.
Why do people keep claiming that is more profitable to mine BCH?
Less transaction less block chain growth. everything is good for something. ETH have now 250 GB blockchain and ETC 20 GB. A year from now ETH will start having huge problems because of their blockchain size, while ETC will have zero and all solutions ETH will implement, ETC will take and reduce its already small blckchain.
Bottom point is things are never just positive or negative but they are mix of both. Question is what will prevail on long term.