Hi Evan,
in truth, Backup Vault (BV) is not the legacy solution but it is complementary to Recovery Services Vault (RSV).
Some of the key differences are: BV supports some datasources that RSV does not support (Azure Blobs, Azure Disks, Azure Database for PostgreSQL servers); BV does not transfer data to vault storage for long term retention, it only works at snapshot level (you are only charged for the delta storage costs, not for backup storage).
You should use either BV or RSV depending on your datasources and in some cases you will use both.
Hope that helped.
BR,
Alessio
See Also
What permission does a user need to rename a file or folder?How to create a Folder without any name and icon in Windows OS? - GeeksforGeeksCan't open an Office file that has a long folder name - Microsoft 365 AppsHow 1Password is designed to keep your data safe, even in the event of a breach | 1Password