[evdev]

I got burned doing 80-90% of the four-person semester-long software engineering lab.

I think it boils down very simply: the intra-group dynamics can't be opaque to whatever mechanism regulates the group. Hence making the group dynamics unknown to the instructor but not providing group members some other mechanism does not work.

Letting students punish/fire each other would just open up lots of other ways of things being unfair that would need their own mitigations. (In the real world this takes the form, very imperfectly, of a boss' incentive alignment and employee exit.)

I think the only reasonable answer is to not make individual contribution opaque to the instructor. Git/etc (for code and documentation) may be your friend here.