i think ppl r confusing pre-update pack leader with post-update pack leader.
was: a way to instantly heal ur pet to full. tho can only go so far cuz ur pet will start getting 1 shotted if u go long enough in a game.
now: if ure a melee main (especially now with auto melee), ur pet is now in god mode since at full health, it gets overGUARD which itself has a 0.5sec gate period
for most ppl, they should probably swap over to one of the new companion bond mods to reduce death timers. otherwise pack leader is a huge nerf. but also a huge buff if ure a melee main