Wondering other opinions about Tanks

So after a few games recently it has come to my attention that there are many "bruiser" champions in the game. It is safe to say that champions such as garen, darius, and illaoi are among the few that people complain about, and could maybe use a nerf here or there. But Im wondering why champions like Volibear and Gnar and Malphite are able to build full health, with little to no damage in runes or masteries, and still do as much damage as they do. This may just be a person complaint, but I believe that if you are going to dedicate your 6 item slots to being a full tank to defend your team, that you should not be able to dish out insane amounts of damage. If an AD builds assassin like, or just adc building full damage, they should be doing the damage they do because it is on paper "Here are my damage items to account for my damage" but with tanks, they just shout "Look at me, i build 5000 health and can still 1 shot your ADC and Mid!" If anyone else is wondering this or would like to complain about me or this topic I would love to see comments :D thank you