They shouldn't have had a numerical scheme, numbering them robs them of their value.
First they had Super Saiyan, then Vegeta and Trunks chose bulk at the cost of speed while Goku and Gohan chose stamina conservation, that was cool.
Then when Gohan gets Super Saiyan 2 it could have just been written as his latent power, more strength at the cost of stamina burn, then just write in Goku and Vegeta getting that later. Three can just be written off as something Goku bullshitted out when he had infinite energy while dead.
Then you can fix the God stuff by calling it "Saiyan God" and "Super Saiyan God" respectively, the idea of having God Ki, and then forcing that into a Super Saiyan state.