If by "scalability", you refer to the ability to handle a growing number of transactions efficiently, then it does not.

It is very difficult to succinctly summarize this in a few words, but here's by best attempt: Proof-of-Stake requires no energy, so there's little to say about that. Proof-of-Work, however, is an interesting mechanism. While it does require the consumption of decent amount of energy, it also incentivize on the development and adoption of cheaper energy, like renewable. So, even if both mechanisms produced the same result (which is not true, as Proof-of-Stake is fundamentally flawed), Proof-of-Work may be a net benefit for the environment.

Those with the most coins need to be trusted on not attacking the network, or need to be trusted on properly protecting their coins in the scenario of a hacker compromising them, and using their votes for his advantage. Pretty much worse security than Proof-of-Work. Also, the "vote pie" can be divided into more pieces, as long as those with the most coins are willing to sell them.

A malicious attack can be carried out regardless the mechanism.

AFAIK, validators just use their coins to vote on the order of the transactions. The incentive is that, those with the most coins, would rather have the network stable, and not attack it, as that would undermine their wealth.