I think that matches as well Toriyama's view, Gohan was stronger only when he fought, but
Goku is a Saiyan and the real protagonist for the final battle.
However Pure Buu only was serious against the Genki-Dama, so it's hard to say how much Goku is strong. But:
In Dragon Ball super,
Vegeta just became stronger mid-fight in very short timeframes, if against someone stronger.
Kid Buu was playing with Goku, that might allowed him, to catch up.
Another misconception is that fans someone thinks Toriyama ever stated that Gohan should be stronger, but the only words that came out from Toriyama mouth is that,
Goku is always the strongest.
Toriyama also stated that in a manga, the new enemies must always be stronger than the previous otherwise the reader won't be satisfied, if Kid Buu was weaker, how would a reader be satisfied?
As matter of fact, Toriyama also stated that both side during the Majin buu arc, were keeping transforming to became stronger and stronger. If Buu transformed in Pure buu at last, how can he be weaker if both side keep get stronger?
This fully matches Toriyama's logic, remember he said new enemies must always be stronger.
SEG which also recaps all the event up to Pure Buu from, in chronological order, super buu, gotenks, buhan, vegetto,
lastly stated that the Buu Goku was fighting was a powered up version of Buu!
So Goku was fighting against something stronger than Buff Buu which is even way stronger than Super Bu! That's more impressive than anything Gohan did.
Hence he can't be weaker!
It's hard to say, how much strong is Goku, he's definitely stronger than Gohan, however there are lot of information that say even just manga-wise, Pure Buu is the strongest.
This, even ignoring, like dozen of anime related sources that are still official material which blatantly confirm all of this on a whole higher degree, they just amplify this a lot, as usually anime does.
The authors of Dragon Ball KAI stated they wanted to be absolutely faithful to the dialogue of the manga, but they still wanted to keep all the dialogues that put Pure Buu above every other Buu.