We recently received an email asking about network inconsistency. The reader has 60Mb/s internet access, but their Wi-Fi network often drops anywhere from half to a twelfth of that. They have Ethernet in their home, but use a version of powerline networking, which carries about 30- to 40Mb/s.
They asked: “Would it be possible that OS X (or other software) constantly observes speed performance and, if performance is bad, automatically switches from Wi-Fi to Ethernet?”
The reader is aware that if the connection drops altogether, macOS will swap to the next available network connection, if multiple connections are active.
It’s a great idea, but it doesn’t exist. Conceivably, a developer could create software that monitored network interfaces and changed the priority of which network was used when one dropped, but…