Backup rate decrease

Recently I added 3 servers to our network (all OS 2019).  One is running BE 22, the other 2 are backed up via remote agent.  Initially the other 2 servers were domain members and were running nightly full backups at rates around 1100mb/min.  After promoting them to AD DC's their backup rates dropped to around 350mb/min.  Aside from promoting them to DC's there are no other changes that have been made to either server or our network and there are no errors or signs of other issues.  I'm just curious if there is anything I can/should look at to improve backup rates?