Gravity is not very different between the ground and 35k feet. The term “Zero Gravity” in space is misleading. There is plenty of gravity outside the atmosphere. Being in “Free fall” is a more accurate description of space flight.
The reasons to launch by drop are 7 miles of altitude - potential energy gain - you don’t have to carry the fuel for and the much thinner air takes less energy to accelerate in.
That is the goofy thing about the “Zero G” experience Branson is selling. Its basically just taking you up to high altitude and dropping you. Unlike Orbital Zero G where you are falling towards the earth while the earth curves away below you, so you never hit it, you are falling towards earth just like a guy committing suicide off of a building.
Not too many people would pay $200K if you describe it like that, I’m afraid, however.