But, "they" can join themselves to control Bitcoin, why not? It's not impossible and free market allows this. All depends the will of each one of the members of "they" group (chineses). If they want they will be partners on it to try rulling Bitcoin to make big money while the only thing another people can it to follow their lead trying to predict what will be their steps.
If the chineses living in different houses join one only big house they will be stronger and more influential over crypto-currency world, over Bitcoin.
instead of spreading out the hash power to give the smaller guys a bigger chance and themselves hurting each other by being separate by competing against eachother.
you would see one pool. ensuring block rewards with every block. if your mindset had a chance of being onto something.
all the technical reasons about your mindset have been done to death for a few years.
think about it in the mindset of all of the segwit/dynamic block talk. even if something malicious/intentional was to occur, user nodes will orphan a malicious block of rule breaking data.
at very worse the block production from a massive superpool doing something malicious can be blacklisted and orphaned off.
but when you say "they" you are not talking as if the rational conversation is about say 100 people spread over 3-4 pools.. managing mining farms in 10-15 locations hundreds-thousands of miles apart
your talking as if its 1.3billion people all in it together eating the same bowl of rice.