At this moment, you need about $400-800 million dollars to attack the $44 billion Bitcoin chain (and in PoW too, you can get some or even all of them back by short selling in the right moment).
This $800 million sounds about right, but can you source or show how you calculated this number?
This makes PoW seem way less secure than PoS.
PoW is also a huge pointless electricity drain on the world, already using more electricity than Iceland, the country.
If prices go 1000x higher as we like, it'll be 1000 Icelands, or entire continents of power just for PoW.
PoW therefor seems to have no future.