That's not true. SMR drives perform worse all over the charts, regardless of file systems. Especially writes can bring it to a halt. There's a lengthy article at Ars Technica that shows thatI recently bought a Synology two drive NAS for a client as a package with drives. Had the option of WD or Seagate drives. I chose WD as I trust their reliability. The drives were SMR. After much research I learned that SMR drives seemed to only have issues with ZFS and Synology does not use that.
You should be OK with your WD drives.