Lord Brofist said:
I have Gotenks around a 1.10x or so weaker than Gohan and around a similar gap give or take between Gotenks and Super Boo. SSj3 Gotenks had a pretty notable advantage against Super Boo, though obviously not to the level that Gohan had.
Essentially in the end, the difference between Gohan and Gotenks is that one of them beat up Boo a bit more.
I'd say the difference between Gohan and Gotenks is a bit bigger than you think. The only one who said that Gohan was a little stronger was Trunks, who first tried to overstate the fusions power.
SSj3 Gotenks only took control of the fight once he got serious. But then we have Buu saying that he wasn't serious either after the fact.
Granted most of that can be chalked up to villain arrogance, especially since he seemed pretty bad off right up until Gotenks fusion wore off.
If he was playing around, it sure made him look stupid to do it with someone who at worst was about his equal. The only conclusive thing we know is that Gotenks going all out was beating a possibly non-serious Super Buu, who was more or less even with a jackassing around Gotenks.
It's also possible that Buu meant by not going all out was that he wasn't pulling all the stops to actually kill Gotenks, that he was still using all his power, just not apply his full effort in terms of skill.
Given the context and so on, it is still reasonable to say that Gotenks was strogner than Buu, only not a massive blowout.
I'd say a 1.05-1.15x difference at most.
Contrast that to Gohan, who casually manhandled Super Buu, doing more damage in less blows than Gotenks ever did, with no ki attacks. This is also on a Buu who was without doubt willing to try as hard as he could. A Buu who still knew that while he had a good chance against Gotenks, that Gohan was likely so far beyond that he'd need to absorb someone around his own power to be able to dominate.
So if Gohan were to fight a SSj3 Gotenks that was out for blood, he'd still stomp him just as bad as he did Super Buu. The only difference being that he'd need to put a little more effort into it, and that Gotenks would stand a better shot of getting a lucky strike or two in.