current Hash Rate:

• https://fork.lol

Relative hashrate (period averages)
                BTC      BCH
6 hours        83.02%   16.98%
1 day          87.36%   12.64%
7 day          87.68%   12.32%
30 day         88.61%   11.39% 

if you start comparing the price from Bitcoin to Bitcoin Cash, you will see that the hashrate is always around the price ratio. So if the Bitcoin Cash Price goes up, so will the hashrate (Miners want to profit). ==> https://cashvscore.com/

so a small group BTC miners can easily attack Bitcoin Cash, while BCH miners can hardly influence Bitcoin.

is not true as Bitcoin Cash difficulty adjusment is way faster than Bitcoin Core's, it is not even listed on fork.lol (does not make any sense)

Difficulty retarget                    
                                BTC                BCH 
Date (24h UTC)           Jun 20th, 21:50             -
Remaining               1 week (880 blk)             -
Change                         -6.99%                -

so keep in mind that if miners "leave" from BTC, it will take longer to adjust as less miners are trying to solve blocks i.e. it takes longer to solve 880 Blocks, can take 10 days, 14 days or even more if more miners leave (death spiral)

why should they stop mining and try to double spend (which is not possible, or do you have any proof / did you test it successfully?) on another chain and lose profit / help another chain with a loss?