The fact of the matter is: You won't scale as hard and as strong as your carries will.
Sure, in gold or silver, it might be enough to get all the kills and carry the game through sheer brute force of numbers. But as long as you do that, your teammates won't be able to work to their full potential. In other words, not only are you not contributing as much as you could, you are holding your teammates back
So what are you supposed to do, as a Jungle, Support, or Bruiser? Well, this is where mechanics and skill come in. You may not be able to have the most optimal items, but you can still play your champion to their fullest. A good snare can turn the game around. A strong aura - carrier can give your team the edge in teamfights.
It's not enough to just build items anymore: You need to learn how to use your skill too.