The game does a terrible job to teach new players how to heal.

[Arohk]

I am doing mentor roulettes, and i ever so often get healers in my dungeon group that do no damage at all, they just stand around and do nothing or keep producing overheal despite no one taking damage.

I don't understand how it is not obvious that a healer also has to do damage if there is nothing to heal, especially on dungeon bosses.

And yes i have tried over and over to tell them, most of the time there is no reaction from people or they don't speak English.
There was one instance though where a german player actually listened to me when i told him to not use Adloquium all the time and to damage instead, (it was on lvl 80).

So either make the game teach players how to play a healer properly or change how MP generation works, increase the MP costs of heals but let attack spells generate MP instead of costing MP, that will force even the most learning resistant person to cast damage spells or they will run out of MP very quickl.
As a trade of, basic healing spells like Cure and Physik could be free.