ADC is the best role to carry out of Bronze.

You probably think playing the big burst, scary assassin mid-laner is your ticket out of Bronze. But how many games have you played where you push your laner out 2-3 times and maybe get a kill or two...meanwhile bot lane is feeding Vayne like a pony at the fair.

Guess who is going to win?

After 20 minutes your ability to impact the game on Zed will diminish. Especially if your team is too stupid to let you split push(it's bronze). But that fed ADC is going to be turning out Tons-of-Damage in every teamfight(it's bronze...all you do is team fight in mid lane after 20 mins). You might be able to get a pick or two, but unless you can get to that ADC every fight he's going to be carrying his team.

Some will say you need a good Support to succeed as an ADC...Not in Bronze! most Bronze bot lanes won't punish you that hard for having a weak support. And if they do, just let the wave push and farm under turret.

Bottom line: Almost every bronze game almost invariably makes it to 30+ minutes regardless of how fed the mid laner gets. At 40 minutes the ADC is the king(or queen) of damage and will repeatedly win those repetitive mid-lane teamfights that consume the late game in Bronze.

Reference: took me 400 games to get out of bronze playing mid lane last season. Did it in ~20 this season and I just started playing jinx like a week ago http://www.lolking.net/summoner/na/31278272#profile