One of the arguments against proof of stake is that those with the most stake maintain power over the system (much like our current financial system) and therefore is not "truly" decentralised.
Can't this argument also be applied to proof of work? Those with most wealth can accumulate the most mining hardware and therefore have most control over the system?
I think the point you raise about poof of stake and proof of work having a similar challenge is true. Depending on who you ask, both types of security can be described as both decentralised and somewhat centralised.
In terms of proof os work, yes, technically there could be a person/s that may have a bigger control than smaller miners due to their resources but this challenge of some miners having monopoly over the network at any one time is kept under control by introducing several penalties if they were found out. Penalties, include not getting any rewards for their mining, blacklisted and never being able to be part of the security network again, etc.
And, let's remember that consensus from lots of different computers around the world is required to agree on any one transaction, thus limiting the chance of mischief.