i can answer this to you…
playing mercy is very relaxing compared to other heroes.
sure you need to stay alive… but you need to do this with every hero.
the beam makes the gameplay very easy and chilled… most time i played mercy when i wanted to have relaxed games… and ofc im gonna play mercy when the enemy team is running mercy everything else would be a disadvantage.
shes an easy hero that can do a lot … you can easily be helpful… and feel good about it.