A consensus algorithm that uses a combination of tier 1 PoW mining like BTC when combined with staked tier 2 PoS full nodes (e.g. Dash Masternodes) with the application of chainlocks does add additional security.
It also vastly improves the security of zero confirmations over that of bitcoin-core. Dash rotates its chainlock quorum of 400 masternodes trustlessly from a pot of ~5K every 24 hours using BLS signatures. Dash rotates its InstantSend quorum of 30 masternodes trustlessly from a pot of ~5K every 24 hours using BLS signatures.
(edited)