Whatever equipment you buy will lose it's value quickly, in 5+ years, it's probably worthless. And that's ignoring all the money you have to spend on electricity, non-stop and increasingly. In PoW, if miners slow down, they'll become irrelevant.

Even if you manage to acquire a 51% hash rate for example (which is extremely difficult), it'll be very difficult to keep it over a long enough period of time.

PoS is fundamentally broken in my opinion, it literally says "rich gets richer" and wealthy stakers will get higher (absolute) rewards which they don't have any incentive to sell since they didn't spend any energy to get it. That's even ignoring all the custodians which have large quantities of the said crypto, so they can just keep the rewards to themselves or keep a sizeable % of it.

One of the motivations for the DAO hack hardfork btw was that the attacker would hold significant power under a PoS system.