You forget that Miners will choose the chain were they can make more profit. If Bitcoin Cash (BCH) Price is in relation higher than Bitcoin Core (BTC) Miners will move to BCH, doing more profit.

Miners can not really jump over to BCH and try the attacks you mentioned. Hashrate will be adjusted way faster in BCH than BTC, so it will be (if even) a very short time where they could try todo these attacks / doublespends.

About propagation time, in the end the (honest) majority will ignore the bad miner and his wrong block, he will loose money from his wrongly used hashpower.

0-conf does work and is fast(-instant), nobody will try to double spend your coffee when he needs to invest a lot more than he can win (your money from the coffee).

If you gonna sell a house with Bitcoin Cash, you can easily wait for 6 transactions to be sure.

0-conf works for micro transactions, nobody is going to pay 10 dollars for 0.00000001.

I prefer my Bitcoins in my own "private key" Wallet on the blockchain. I don't want them stored somewhere in another layer linked up to the blockchain.

Why should I want to leave my money at the supermarkets place for the next time I go shopping?

Bigger blocks will give problems over time and multiple coins with the same mining algorithm is a bad idea anyway

Why will a bigger car / plane / ship / harddrive... give more problems over time than a small car / plane / ship / harddrive?

Why is it a bad idea to use the same techniques as a competitor? Why is it bad to use the same wheels as another one?