The fact that ZERO PoS systems have been attacked, even though many of them are tiny, speaks volumes about PoS security. ALL of your attack vectors remains a theory at best. If you want to prove your point, the best method is not theorycraft further, but actually go and attack one currently public and working PoS system, you can even pick a tiny one if you wish.
Security through No One Gives a Fig.
That's a new one.
Not really, many tiny PoW systems have been attacked, actually being tiny increase the likelihood of an attack for PoW systems.