That kind of attack could be indeed the most effective way to destabilize Bitcoin, much more effective than a ban, but still is an attack that becomes more expensive to perform year after year, and the final outcome is not clear. Let them try, this experiment has to be proven and tested under all kind of stress. I have plenty of popcorn.

Also, it's pretty presumtious to assume "year after year" would even be necessary. But this is the speculation forum.