Actually the weld WAS shielded by the CO2 from the Oxy-Acetylene flame. The shielding gas is the product of combustion.
If you remember if you adjusted the flame oxidizing then the excess carbon was burned out of the steel and the weld was hotter, but perhaps not as pretty.
The combustion gases from a neutral flame is what shields the weld and makes pretty welding possible. Deeper in the puddle the Purer the metal. Try electric welding without shielding from flux or gas.
There is no inert oxygen I know of. Being a certified aircraft welder with an A&P license
with Inspection Authorization I know a small amount about welding.
It is but this is a place where these parts should be joined by bolting. I would guess that very few hitches are welded since it would be difficult to make sure that it met design specs where the strength of a bolted unit can be determined closely.