This is just not true and anyone that played before mass rez got removed knows this.
Mercy was not made to pocketbot, and in fact pocketing a hitscan was seen as throwing. Reducing her HP made her even more of a pocketbot because now decent DPS players can pop her even easier if she tries to heal anyone that isnt a 30 range hitscan DPS.
She was made to be a mobile flying healer that farmed her whole team’s wounds to min-max her ultimate’s uptime and deny the enemy winning teamfights.
Unless your definition of ‘‘pocketing’’ is simply any single target healing, then thats a you issue.