I think the difference is there are a lot more mage items that have defensive stats snuck in, and mage abilities are a lot stronger than adc abilities.
In older versions of league, battles would last slightly longer, and tanks and supports had a lot less damage and couldn't solo people. So it was easier to DPS because you had more time to DPS.
Right now its a weird spot where the only way some carry classes can by viable is if they have nuts amount of lifesteal. In general, healing is nutty high in league right now to deal with the nutty amount of free damage.
Do you think Legend: Bloodline is a healthy rune? because to me who's played for so long it seems absolutely nutty to get 12% lifesteal from runes. But its almost a necessary bandaid fix for the crazy high burst damage that is cheaply available to everyone.
Edit: What do you think of this? ...