Projects based on a Proof of Stake algorithm have tackled many of the scaling issues of PoW by achieving better latency with less computation, bandwidth and storage.
Scalability in terms of computation is determined by the amount of time it takes to verify transactions and their signatures which has nothing to do with PoW and is not improved by PoS.
Scalability in terms of bandwidth and storage is affected by transaction size and has nothing to do with PoW and is not improved by PoS.