PoC is not a replacement for PoW; there is nothing at risk of loss during block generation. At best it is an alternative to PoS.
I wrote some larger posts about that somewhere in the Altcoin section (btw, I would really like a coin-neutral "Cryptocurrency Technology" subforum, because this section is normally dedicated to Bitcoin). There is less at risk than in traditional PoW, but not nothing; the point is that if PoC was carried out in an "industrial" fashion like Bitcoin mining then the loss of failed hard drives would become a major factor.
Nevertheless, short-range nothing-at-stake can be a problem, but long-range attacks should be costly.
What is the point of replacing energy + ASICs with hard drives ? Do you really want a single botnet to be able to 51% attack your coin so easily?
That is only a problem while "PoC hashrate" is low; if it was carried out in industrial fashion like mining, legit actors would operate such high capacities that botnets would not have a major influence.