Why do defensive stats do literally nothing?

It really does feel like building tank doesnt matter anymore and that building full damage at all times is the way to go. If someone on the enemy team starts getting fed and I try to build defense stats to counter it, it doesnt matter and I still just get melted. I really miss when someone getting a few kills early and going hyper damage wasnt the only way to win and you could actually build defensivly to counter someone getting fed.