Kaioshin seems to think so.
Chapter: 479 (DBZ 285), P5.2-4
Context: when the Z Sword breaks, after Gohan trained with it for a day
Gohan: “But…thanks to that, my arm strength has increased a lot. That Z Sword was incredibly heavy, after all…Perhaps this was what they meant by me obtaining the greatest power in the world.”
Kaioshin: “I-I get it…If he’s acquired that much power in his regular state, then if he becomes a Super Saiyan it will become an even more substantial power-up…! Ye-yeah! That’s it! That’s definitely the greatest power in the world…!”
Goku: “…But…Is he greater than Majin Boo?...I wonder…”
Just reading the text Gohan sounds sarcastic (like he's saying "Yeah, my arm is stronger, big deal"), but Viz and the art he looks dead serious about it. Yeah, it was a good training and he's at least above Goku who can barely swing the sword.
The big deal here is Goku's line. Does he say "dunno" because they're close, or because he doesn't know how strong SSJ/2 Gohan is? Can you look at a Base Saiyan and tell how strong their transformed form is?
DBS manga does have Future Trunks struggling with Future Dabra, but different people rarely get the same gains from the same training (Compare Goku's Kaio training to Piccolo's) so I think we can ignore that.