What's the exact story of jupiter and our earth, not becoming a super-earth?
Your reasoning is wrong: you cannot extrapolate from the outside of a sphere of matter to the inside of an annulus or a shell of matter. The gravitational pull of a uniform annulus of matter is 0 inside that annulus.
See the wikipedia article for more details on that theorem.
So having a disc of matter around you is not the same as having a sphere of matter next to you.