I think Ctrl-a is for "screen", which was my first multiplexer. I'm also tempted to change it, but there are so many different systems that I ssh into in which tmux is installed and my bindings not, so I've made peace with using Ctrl-b :-)
Oh, wow... haven't thought of 'screen' in ages - my first <coughs> as well!
Alas, I don't ssh anywhere anymore. I was an SDF user for a couple decades, but eventually found I could do everything I really needed (especially as needs dwindled) in whatever Linux that Chromebooks provide. And now needs in that realm are evaporating one app molecule at a time.
These days I can be fine anywhere I can have Vim and Lua in a reasonable scripting environment (even "cygwin"...).