alt Hacker Newsgit rebase -i drops you into a text editor where you have to manually copy, move, and edit lines, knowing what words mean what and manually type them each time.
hg histedit gives you a TUI which shows an interactive list and allows quick manipulation with the arrow keys and single characters for actions.
The two are as "equivalent" as i3 and KDE.
I don't know what version of hg you're using, but the histedit I've used drops me into an identical text editing setup as git rebase -i. It includes a summary of what the verbs mean in a comment at the bottom.