I'd like to add to your #5. If Google deems you a legitimate threat, then they can just de-crapify their own search for a bit by going back to their old algo. It's extremely easy for them to fight back.
Is that true though? I think a bit part of the algorithm evolution is to combat undesirable forms of SEO. I would rolling back the algorithm to some older generation would make the results quite spammy.
That would be a victory for users.
A temporary reprieve, more like. Google will just wait for the competitor to fail and then go back to their old ways.