Hi,
A verification guarantees that the backup data is still all there and valid and could be, at time of verification, restored to the same state it got backed up.
That may not be the same then a restore resulting in a working VM/CT setup, e.g., if one missed backing up one of the virtual guest disk, or if the storage of the virtual guest was already corrupted when the data got backed up.
Those risks are unrelated to Proxmox Backup Server, and it cannot really check that.
That's why periodic end-to-end restore tests will always have value (untested backups are more a gamble than anything else).