> what happens if you onboard a superstar that works with django some other way

If you hired a "superstar" that goes out of their way to hand-write migrations in cases where Django can do it by default (the majority of them) you did not in fact get a superstar.

I have yet to see anyone hand-roll migrations on purpose. In fact the problem is usually the opposite, the built-in migration generator works so well that a lot of people have very little expertise is doing manual migrations because they maybe had to do it like 5 times in their entire career.