1) Out of the two fighters available to fight Buu, yes, he was the only one of the two that could. Vegeta couldn't, and that was it out of their options at the time.
Vegeta is the one who said it and he's a dead person so purely by context we know being dead isn't it an obstacle. Secondly Goku was also dead just a few minutes ago too. Thirdly Vegeta wishes everyone back to life. There any number of ways Gohan can fight Kid Buu and the very people in this conversation are aware of multiple ways to do so.
And again, If you dislike how I'm presenting this narrative then check the official Manga guide and both versions of DBS. They corroborate this narrative. Daiz says Goku is fellow strongest with Kid Buu. DBS anime tells us Goku is the strongest Saiyan and the strongest after Buu was defeated and it confirms the OP nature of the Genki Dama. DBS manga starts with a recap of how only the Genki Dama could stop Kid Buu and now we have this VJump scan. Even the BoG movie has everyone at their strongest and Vegeta only surpassed Goku when Bulma gets slapped. This is not just my interpretation. It's repeated and corroborated time and time again.
3) Gohan only donated genki, so that's not remotely telling about how he could have done if he had fought Buu normally. What he donated was only a portion of his total strength.
Kid Buu deflecting the Universal Genki Dama shows us he would deflect anything from Gohan because Gohan can't generate anywhere near that level of power by himself.
4) Fellow strongest, meaning Buu himself. It's all the same Buu. From Evil Buu to Gotenks Buu to Gohan Buu and so on, it's all the same Buu.
It's not. Goku salutes Kid Buu as a guy who fought everyone by himself and still went the distance. Goku by contrast views Super Buu as a cheat that resorted to unfair tactics like absorption. He also never salutes Fat Buu in this way even though he's lying down right there. That section of Daizenshuu is dedicated to the destruction of Buu and in that section only one Buu is destroyed and Fat Buu is still alive. You can't deny that it's identifying Kid Buu specifically because it's literally identifying him by mentioning specific details.
Why is it the fandom and various DB media have been able to identify specific versions of Buu for decades but you're apparently insisting that we can't identify Kid Buu specifically here? That's a serious question because you're using a double standard. What do we need to do to specify a specific version of Buu? Having a picture of Goku saluting him isn't enough. Saying Goku defeated him isn't enough. Putting an entire section in Daiz about how he was destroyed by a Genki Dama isn't enough. You just refuse to acknowledge anything the specifies Buu but you're fine if it identifies any other version of Buu elsewhere. That's a double standard.
And nothing in the Pure Buu part of the story contradicts Evil Buu being stronger. Nothing. The Daizenshuu's information is both vague (speaking of Buu in general) and also skewed by filler content in the anime. Nothing in the DBS anime/manga says Pure Buu is the strongest (what you've shown as evidence doesn't say as such), and this current V-Jump article is already contradicted by Toriyama's statements, as it says that Bibidi created Buu, when Toriyama established that he didn't. Since that information is faulty, then that puts everything else into question as well. And since the Gohan Buu = Super Saiyan 3 Goku is contradictory to established fact anyway, there's no reason to give it any weight at all.
First of all I'm citing Daizenshuu's manga guide so filler information need not apply. Second of all the VJump article is merely repeating the Bibidi information from the manga so there's no problem because the original manga is wrong there too.
And yes, there *is* evidence in the Kid Buu saga but you refuse to acknowledge it. I've explained that evidence multiple times now and you keep saying it doesn't exist. I say everyone ignore Gohan. I say only Goku can fight Kid Buu. I point out that the incomplete Genki Dama with Gohan's power isn't enough. I point out the Universal Genki Dama can be deflected by Kid Buu. I point out Goku saying without Satan and Good Buu everyone dies. I point out how Goku trains for 10 years and still wants his full power agains Uub.
Your answer to all those pieces don't count or don't mean what I say they do. To be blunt that's just your opinion and we're both just random fan's. You can say they don't mean what I say they mean but in the end, your opinion carries no weigh. That's why I cite Daizenshuu, the official Manga guide. So if I say it means something, you can ignore me. If you say it means something I can ignore you. But the official Manga guide carries more weight than you and I. It's not a matter of your opinion at this point. This is further emphasized with how BoG, DBS manga, DBS anime and even Kai all reinforce the Kid Buu and Goku narrative.
If you say the manga never said something but the official Manga guide, DBS manga, DBS anime, BoG and Kai all say otherwise, who should we believe? You or all those sources? To be blunt it's your opinion against 25 years of additional information.