Not saying there isn’t a performance issue here, but note that there will always be a bottleneck. No matter how much you tweak, something will always be slower. That said, are the speed of your backups for the amount of data that you are backing up and considering your source and destination and change-rate of your data, are you getting the performance you would expect? It can be misleading seeing a bottleneck when everything is working great, so aside from following the best practices to make sure everything is tweaked as it should, is the backup performance meeting your expectations, and meeting your needs?