prop is definately not a route into a bulge bracket. thats not to say it cant be done, but if you want to go IB you're better to start IB. Prop and IB are two very different trading roles. Its the difference between running your own business and have a 12hr a day job with a pay check and bonus.
IB's want a yes man.
They want to train you to do their thing their way.
They don't want any creativity. (ala SocGen)
They want you to produce. You don't have to make a lot, just consistency.
They don't want you to lose money, not even a little bit.
If you have experience, that's a strike against you.
If you "know" the market, that's a strike against you.
If you have an opinion, that's a strike against you.