@HAALD well in games its usually like this
The most dmg takes aggro but tanks have 2 ways to take it besides that
1 their skills generate more aggro for examle say he does 10 dmg but his skills generates 10 times the aggro so its like he did 100 dmg while the attacker would do 70-80 in the same time
2 option is taunt which usually works diffrent in most games some instantly give you an enourmus amount of aggro like worth 10000 dmg or something
Others have a duration and all aggro inflicted in this time no matter from where gets directet at the tank
There are even more ways to do this but it would get to long^^ also healing usually gets more aggro than dmg