But they lived for 150-170 years! And they suddenly start dieing every 12 months when you recruit them. Massive extinction of them! And it really doesn't matter if they get N1 or N4. With N4 old age starts at 150 and the youngest one you will get will be 155 years old.
Possibly if crones could get to W2 or E2 with a reasonable possibility (say 10-25%+) they could branch into lower-mid W and E via boosters. And they should still lose the old age.