What Is the Main Security Benefit of Combining PoW and PoS in Proof-of-Activity?

The main security benefit is achieving a higher level of decentralization and attack resistance by requiring two distinct types of resources for block validation. PoW miners expend computational power, while PoS stakers lock up capital.

This dual requirement makes it significantly more expensive and difficult for a single entity to mount a 51% attack, as they would need to control both a majority of the hashing power and a majority of the staked currency.