Backblaze/general routing table performance problems?

I'm trying to configure my Windows routing table to allow Backblaze to circumvent my VPN by adding static routes to each of Backblaze's published server addresses.

I added each address to the routing table, bound to both my default (local) gateway, and physical network adapter.

ROUTE ADD 162.244.56.0/21 192.168.1.1 METRIC 2 IF 14 -p

Now my backblaze traffic is successfully bound to my physical network card, but my performance drops from ~15-25mbps up to ~1-5 when my VPN is connected.

Is there something silly I may have forgotten?

Backblaze uses a windows service, rather than the desktop client itself, to do the actual uploading, so I don't know how else I can bind it to the desired interface.