Half-blood Saiyans are stronger than full blooded Saiyans. This is confirmed cannon:
Vegeta: “At any rate, the battle power of Kakarot’s son is unusually high, even by the standards of Saiyan children.”
Nappa: “Maybe his reading was wrong.”
Vegeta: “No, it wasn’t wrong. Raditz really took a large amount of damage from that brat’s attack. It seems that mixing Saiyan and Earthling blood begets a powerful hybrid.”
That's why Gohan, Trunks, and Goten all mastered Super so young.
Gohan in particular is abnormally stronger. According to Vegeta, Gohan could be stronger than his father or Vegeta, if only Gohan would train more.
At the end of DBZ, Gohan was the strongest non-fused character. In his base form,he was stronger than SS3.