Why does tank Ekko still output DPS damage?

Firstly, DPS = Damage Per Second so he has the right to output damage per second, just it shouldn't be high.

Secondly, check his abilities and scaling, except his ult (at 130% ap) his scaling are bad to average (10% on his Q and 20% on his E) the return on his Q is the average one at 60% but you are supposed to dodge it anyway.

So the reason is simply, his base damage is ridiculously high for whatever reason and if you build him tank or AP makes no real difference since the scaling on his heals on shield are good enough to keep him relatively tanky anyway, the only difference perhaps is that if you go AP you rely on your abilities more but you are a tad more brusty, if you go tank youa re less brusty but you don;t really have to hit your W or R to survive (which are the main "counter"to ekko)