I can't help with your problem, but I wanted to say that I updated Excel 2016 from 16.16.4 to 16.16.5 today in Mojave 10.14.2, and I've experienced no issues with either. (I also ran 16.16.3 in Mojave, but I can't be certain if I installed Mojave over it or updated to it after I installed Mojave.)

Also, com.microsoft.word doesn't exist on my installation either...visible or invisible.

Maybe try this: navigate to /Library/Application Support/Microsoft/MAU2.0/Microsoft AutoUpdate.app and run it; if it updates you, the updated version may work.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire