Kirkland instituted NEP route because people were complaining about career progression and leaving for partnership at other firms but most of those who made the "automatic" partnership got there from billing not having a book - they are not profitable to give equity at other V10 firms or Kirkland. IDK about them leaving the profession though but it would be a corollary.
Every top US firm is going to heavily guard equity and even DPW just moved away from lockstep a couple years back. But yes, other US firms have NEP roles just like most firms because "progression". From the outside it is often hard to tell who has equity too. I think Kirkland is somewhat exceptional in that they give out partner at 7PQE is it?