the best example are all the miners mining at ghash.io with 51+% am i right?

pos/pow have the same problems
no you are not right at all..
miners having 51% of the power to produce coins for very limited period of time is not the same thing as stake holders with 51% of the coins and the power to create 51% of all future coins for eternity.
this is why the vericoin devs had to take such drastic action when someone had a mere 30% of the coins.
also a pool having 51% of the hashing power is not the same thing as a single entity having that much power because miners would simply move if the power was being abused.
pos and pow have very different problems.
i dont understand your argument why miners have only a limited time? do you mean because the network hashrate can increase?
that argument doesn't revoke anything because the entity with over 51% can just buy/produce more hashpower.
even if i give you the point that a pool might not count as a single entity, because miners could leave if the pool acts in a malicious way -
bitcoin is facing the same problem when an entity decides to buy/produce more then 51% hashpower - tbh even 35% is enough, but u should know it if you read the thousands of articles about it.