Suppose you could use a balloon to get to LEO altitude. You're still not in orbit. Anything that actially is in orbit will come hurtling at you faster than a bullet. Most of the fuel used in getting to LEO is used to achieve orbital speed, not orbital altitude. So the question of ground launch vs space launch is really one of where your engines operate most efficiently, or if you can avoid air friction in the dense lower atmosphere, or that sort of thing. Baumgarnter was nowhere close to "10% of the way to the ISS."
A good way to sort of wrap you mind around exactly LEO means is to consider that at LEO altitudes the strength of gravity is, for most intents and purposes (9.0m/s^2 vs 9.8m/s^2), the same as on the surface. If you get up that high then let go, you are going to drop like a rock.
If you want to not fall, you have to keep thrusting straight up, which obviously is not practical. The next best thing is to try to move sideways. Sideways fast enough that you clear the horizon before you hit the ground. You have to move fast enough that when you fall you miss the earth.
Moving that fast is pretty damn hard. Any rocket capable of doing it, even if it is already "up there" is going to be far to large to practically lift with a balloon.
> You have to move fast enough that when you fall you miss the earth.
So what you're saying is that there is an art, or rather, a knack to flying, and that the knack lies in learning how to throw yourself at the ground and miss?
You're right about acceleration being an issue. It's possible that altitude is negligible compared to orbital velocity. I'm not sure what you mean by Baumgartner wasn't 10% of the way to the ISS. The ISS is at 370km, and the jump was from almost 40km. Of course there are other technical hurdles to getting there, but I was only referring to pure altitude.
