It’s one of the core features that rebases, including branch names (bookmarks in jj) work ‘correctly’. You can rebase whole dags, including merges, with multiple named heads with just one jj rebase -b.
note that bookmarks don't float, unlike git branches, so if your pattern is to produce a lot of commits, you'll want something to keep your jj bookmarks pointing to the top of your pile of commits.
this is less of a problem if you're more into the 1 change == 1 commit workflow.
This looks like any other git arcane incantation. If this is a common pattern and jj aims to make things easier, should probably be part of the core commands, no?
It's something that makes a specific workflow easier, a lot of folks that use jj don't necessarily use that workflow.
That doesn't mean it couldn't be a core command someday, but given that the alias works well for people, there's not a ton of reason to make a whole new command. You configure the alias and you're off to the races.
