its the reason why we have testnet4 and will have testnet5 and so on.
There is a major flaw in this logic as well.
If you owned a shitcoin exchange and the threat was "We will make another shitcoin and market it for you" would you be worried about this threat?
I can rekt testnet4 single handed, I can spare a few PHs and point it there just to prove a point, in fact, many other fellow miners can do just that, but then what? you are not going to make testnet4 any better, so all we trying to do now is come up with solutions on code/consensus level.
Point 1 PH at it for 24 hours and see how it does... just don't post you did it here or some asshole will leave you negative feedback!!!