I actually use both. For showing Linux Mint 21 (my goto linux) to newbies, I use the DE.
When I use Manjaro - I am slowly going to BigLinux(!) - I prefer I3.
I agree about the speed. Also, I3 is much less distracting if you know what work you would like to do. Sometimes, just doing stuff with bash makes it easier with I3, less distraction, as I said.