in her old ult mercy could just hide from the enemy team and just rez everyone after the enemy used a lot of ults to kill your team while your team could just not use any , in this way your team have a huge ult advantage from just dying instead of investing some ults as well to win the fight + a well coordonated combo between zarya genji and lets maybe an ana ult being just canceled by a 5man mercy rez is not very fun and neither corect either cuz you can't really counter that (mercy being very fast while she shift + she was invulnerable in the rez animation)



for her rez ability (no cast time + more rezes when poping walk) you didn't cared about positioning , trying to push together cuz you had a mercy that could just fly pass enemy team , rez you and return back . if your monkey / genji / tracer kill an enemy in the backlines and dye in the process (now being an 5v5) mercy can just rez him/her back and the enemy team don't have any real way to counter that , transforming the fight into a 6v5