How much harder would it have been for Felix to use some powered sled and head for the ISS when he stepped out of his capsule? He was already above most of the atmosphere. BTW, Is that capsule still up there? Why don't more missions use balloons for the first stage?
The vertical part is relatively easy, but to be in orbit you need to be going fast enough horizontally, that's around 8km/s in low earth orbit.
The balloon does nothing to help with that. There are launch vehicles that carry a rocket up to altitude underneath a plane and then fire that from 50,000ft. It means you don't need to use the rocket to get through the densest part of the atmosphere, and you always have good weather at the launch height but you are limited to a fairly small rocket.