Hopefully my ramblings won't melt your brains
Basically I somewhat agree with Truhan. I take all this new material portraying the characters in this and that as somewhat "tainted" by Toei writers or what have you.
It sounds completely ridiculous and it probably is, but I personally doubt Toriyama would agree with ultimate Gohan < SS3 Goku, even in BoG.
Back in the manga instead of actually just establishing Goku as the stronger one all along, he doesn't have anyone directly compare Goku to Gotenks and Gohan.
It's only, when the prospect of fighting Super(Evil) Buu comes up, that he has Goku actually admitting inferiority to a guy both Gotenks and Gohan surpassed in strength.
And then later on he has Goku being relieved, when the small one turns up and has Goku refuse to merge, because Buu wasn't anymore either.
The only defining feature of Pure Buu is the fact, that he's the most troublesome/evil one, not that he is strongest, which the anime on the contrary makes a point of several times.
This is what I meant by "tainted" though calling it tainted is a bit silly. When I first read vol. 42, I didn't really concern myself that much with how this little Buu would stack up to the taller one or how it made no sense Gohan and Gotenks weren't brought along, because they were obviously stronger. I don't think it ruins that much, that they put those lines in there, as it's primarily meant to entertain little kids, not for us to nitpick, though perhaps some would question why Goku would want to permanently merge, if he had power exceeding that of Gohan-Buu all along.
It's clear though that lines were added, that made Goku and Pure Buu seem a lot stronger, than they might originally have been intended to be. It's unknown why they would do this, but perhaps they completely bought the premise from the manga, that Goku vs Pure Buu really was the match to decide the fate of the universe and thus concluded, it could only be described as such, if there wasn't anyone else to match Pure Buu's power or that main characters = strongest characters.
To get back to BoG/Super Goku and Vegeta compared to Gotenks and Gohan, it's funny how Gotenks doesn't go Super Saiyan 3 and Gohan was marketed as a Super Saiyan until the movie actually premiered and "corrected" it. I take it the same way as I do Freeza seemingly not powering up against Trunks and Gohan not being at a certain level against Dabra; basically it's done to make other characters look extremely good, Trunks looks like a badass, when he easily disposes of Freeza and Gohan looks like a chump, while Goku and Vegeta look like badasses. It's the same in BoG, where Gohan and Gotenks don't look to be on the level of Vegeta(by Gohan only being SS, at least originally) and Goku(by Gotenks not going SS3 like Goku did).
We have Yusuke Watanabe(it was him, right?) stating that they always intended for it to be corrected later.
To me that just sounds like a bad excuse, not wanting to admit something, but then I'm extremely biased, that I can admit, so due to the lack of better evidence, his statement stands.
The problem for me is that we don't know, what's going on behind the scenes, we don't know, if Toriyama's original script did have Gohan as a Super Saiyan and it really was changed by the movie staff, due to fan complaints or whatever. We just don't, because what Toriyama wrote is not something accessible to the public unlike the manga. When you have the manga it's easy to compare how the mediums differentiate, like Dodoria/Freeza kills Cargo or Future Trunks went Super Saiyan before/after Gohan's death.
Furthermore we have no idea, what small notes from Toriyama, might or might not have been properly demonstrated. For example in Resurrection [F], during the Z-fighters vs Freeza soldiers segment, we have a Toriyama note, that states Gohan is the strongest(this is before he goes Super Saiyan), yet is that little note elaborated upon in the movie? I mean one could possibly argue, that Gohan seemingly does the best against the soldiers, but concluding he's the strongest of the Z-fighters just based on that? I am not sure.
As a little side note, I was pleasantly surprised, they gave away Toriyama's original script to Resurrection [F], but also curious why that could be? Of course my bias tells me, that it just had to be, because they didn't want fans complaining about lack of Ultimate Gohan and basically prove, that it is not them, who doesn't want Ultimate Gohan to be a thing anymore and thus hinting, that the original Toriyama script for BoG did have Gohan as a Super Saiyan and that's why he initially was portrayed as such in the early ads and promotional material
In the end, I'm just speculating, basing my views on what I perceive to be his writing style and some interviews he's given, particularly one, when he talked about limits and thus he came up with Super Saiyan.
I believe that Super Saiyan God is the same deal. As Goku stated in the movie, he could never achieve that power on his own and I think Toriyama considered this was a good way for Goku rewriting what his limits were(and have him genuinely surpass Gohan too in the process).
If Toriyama went out of his way to make it look like pre God Goku and Vegeta were stronger than Gohan and Gotenks, then I just wouldn't hold them so highly.
