The only thing that would make TM faster in 10.14 is if there were separate processes: one process queueing files for upload, the other uploading with maximum bandwidth. This is what Arq does when backing up to the cloud, and in my experience it takes half the time backing up to Backblaze B2 with a 7.5Mbps internet connection than Time Machine takes to backup to a local Time Capsule (and, for that matter, a recently purchased Synology NAS isn't faster either).
It seems as if the Time Machine codebase has not really been updated in the past decade.
I'm using a MBP running 10.13, connected via 802.11ac to the router (which is in the same room).