User blog comment:Braumissomanly/Whats with all the percentage damage?/@comment-24464243-20140817200420/@comment-24792363-20140819194257

I'd just say that it forces players to make more defensive item picks past their first, to focus more on resists than health, and particularly to focusing on counterplays rather than raw champ stat/ability matchup. likely it's also to promote the idea of a non-tank meta, allowing more flexible meta builds. but I agree it is unfortunate for tanks with no counter to range or regen, and that it forces teams to have one or all champs to have this % dmg, or to build a comparable item

however to end I'd say many/most metas focus on burst damage, and though % health is effective, it's mostly just effective on dot-based characters or autoattack % dealers, which are not usually popular in the meta. I'm guessing the idea is youre supposed to be able to lock down and instakill the % health dmg dealers before they can wreak havoc among your team.

putting only % scale and no base dmg would ruin a champs early game as well, when health is low

and as others have said before, op-untouchable-unstoppable-uncounterable tanks are the most annoying shit