>It's not only that. There is also the "replace by fee" stuff that allows BCH to make instant payments with 0 confirmations for small values.

Can you elaborate on this? I did a quick search and the gist of it seems to be that BCH doesn't support replace by fee and bitcoin does, so therefore it's possible to "safely" accept 0 confirmation transactions on BCH because you can reasonably believe that it won't be double-spent before it gets its first confirmation. The only problem I can think of is that there's nothing preventing the attacker (the person making the purchase) from bribing a miner to mine his double spend transaction. Indeed, even without RPF there are "transaction accelerators"[1] that allow you make out of band payments to miners to increase your transaction's priority. It's not too hard to imagine a service where you can pay $$$ for a miner to mine your double-spend transaction.

[1] https://en.bitcoin.it/wiki/Transaction_accelerator