Regarding this paragraph:

The Backup Agent has the same performance profile impact as a secondary. For the initial backup, the load scales with the size of your data set. Once an initial backup exists, the load scales with oplog gigabytes used per hour.

This may not be completely accurate.

We may say "The Backup Agent has the same performance profile impact as a secondary considering only the replication workload.".

We should also add as a consideration, that these requirements are increased by a factor dependent on the number of backup jobs active and running in the same Ops/Cloud Manager group.