why does it seem that in a steamroll game

the adc only damage items without support is too tanky for an assassin that tries to burst them to 0 but fails with ignite too. i seen those a couple of times where base stats of adc tanks a zed ult/combo. why do steamroll games favor that get up where everyone becomes more tanky than the other team due to gold disadvantage. again using damage items= resists more damage. idk i had a couple tilting steamroll games i just wanted to share