Just found this too, through the rust post some days ago...but its quite obvious that from a usability context that btop is easier to use. With bottom you have to memorize all hotkeys wheres btop is showing them right in the interface.
Yea. I was using bottom until I saw this and did a quick side-by-side comparison (nix-shell -p btop, I use NixOS BTW). btop's UI is just so much better.