7 years after defeating Cell, lets say Gohan was equal to Goku was back then and give him a power level of 1.
Gohan- 1
Super Saiyan Gohan- 50
Super Saiyan 2 Gohan- 100
Goku after training for seven years, lets say he got three times stronger in his base form that gives him a power level of 3.
Goku- 3
Super Saiyan Goku- 150
Super Saiyan 2 Goku- 300
Super Saiyan 3 Goku- 1200
It doesn't seem right that Super Saiyan Goku is 1.5x stronger than Super Saiyan 2 Gohan in the Buu Saga.
My power level list is this...
Super Saiyan- 125 x Base Form
Super Saiyan Second Grade- 187.5 x Base Form
Super Saiyan Third Grade- 810 x Base Form
Mastered Super Saiyan- 500 x Base Form
Super Saiyan 2- 2,500 x Base Form
Super Saiyan 3- 10,000 x Base Form
Buu Saga Power Levels
Gohan- 1
Super Saiyan Gohan- 500
Super Saiyan 2 Gohan- 2,500
Goku- 3
Super Saiyan Goku- 1,500
Super Saiyan 2 Goku- 7,500
Super Saiyan 3 Goku- 30,000
It makes sense that Gohan even after slacking on training, still as a Super Saiyan 2 would still be significantly stronger than Super Saiyan Goku.