> introduces some mental friction in walking away???

I don't think it's just mental friction. Suppose you've learned git well enough that everything you do in it is automatic and fast, and the things which aren't fast by default you've built aliases and tooling for over the years. Yes, starting from ground zero you might want something like jj, but at the current point in your life you're not starting from ground zero. Switching to jj means learning another tool to achieve similar outcomes on your workflows.