You need to me careful about benchmarking to find performance problems after the fact. You can get stuck in a local maxima where there is no particular cost center buts it’s all just slow.
If performance specifically is a goal there should probably at least be a theory of how it will be achieved and then that can be refined with benchmarks and profiling.
Sync that has never broken for me and works on a phone. My attempts at keypass with both google drive and syncthing invariably ended up with me needing to periodically do manual reconciliation. I’ve never had this problem with bitwarden. Also, bitwardens passkey hooks work on iOS. They appear unsupported by keepassium.