While it is true the WD Cloud do suffer from a few problems, mostly growing pains I would say, speed over either WIFI or gigabit ethernet is not a function or problem of the WD Cloud, just like the roads and traffic is not a problem with the brand new vehicle that you just bought.
There are no special routers, just routers that support gigabit ethernet, but there are AC routers that give you greater WIFI speeds but still not necessarily the gigabit speeds that we all crave over WIFI.
Another factor is the backup software that runs very slow anyways, but if you compare a USB 3.0 backup to a gigabit lan backup, then there are no comparisons as a USB 3.0 goes at between 80-140MB/s compared to a max speed of about 40MB/s on a gigabit network. Again, network speeds versus USB 3.0 speeds has nothing to do with the WD Cloud device.
Every single NAS/Cloud device will give you the same network speeds regardless of the device.
If you are having speed issues, first check out your network and that everything is running at gigabit speeds. End to end, starting with your router, you can eliminate all connected devices except your PC and Cloud. You should never connect old PCs that has only 100Mb network connectors to your router as this will slow down your whole network.
Check your network cards to ensure they are gigabit cards by clicking on properties. In Mac check system pref and network/advanced and hardware.
Max speed over gigabit lan is about 40-45 MB/s write and 70-80 MB/s reads for ALL network devices. This means a 733MB movie file should copy over to the Cloud in about 15-20 seconds. It will take 10 seconds to copy back the 733MB file from the Cloud. This is mostly true for any device you connect at the other end, including a PC with an attached hard drive.
For a Mac, even though you are on WIFI AC that has theorectical speeds of almost USB speeds, it will fluctuate and is not the best method for copying large amounts of data. There are $50 USB 3.0 gigabit adapters these days that will give you the gigabit ethernet that you need. Make the wired connection, then backup your mac on the first pass, then use the wifi for subsequent daily backups.
I hope this helps