PoS does not reinforce historical consensus. Every subsequent block in a PoW chain makes the history below it more secure because the cost of reversing it is superlinear in the number of blocks built on top. In PoS, this is not the case, the cost of producing a block is a constant, therefore the cost of reversing history is a constant
The cost is offloaded proportionate to the cost of an attack in monetary terms. Its basically the same thing but the centralization of power is horizontally adjusted to bonded validators instead of miners.