It speaks in general. Goku was the example because he is the protagonist, and the only one who has shown all 3 forms.
Do you have any proof of that? Also, do you have any proof that Gotenks has the same multiplier when that outright contradicts what's shown on the page?
Boo had plenty of time to increase his ki. It wasn't stated because it wasn't important, since Gotenks was still stronger, and it wasn't totally unexpected that Boo would be even more powerful.
Do you have any proof of that? Actually, yes, it would be VERY important for Piccolo to comment on that, because Gotenks would go from "strong enough to kill Buu with one blast" to "about as strong as Buu". This would be absolutely critical, and something that Piccolo would mention. Now, show me the proof that he raised his power invisibly without anyone saying anything about it, contradicting his previous actions and his character in the process.
I'm not, seriously. Gohan only proves that genki is a big part of his BP, but we are still in the dark. Not to mention that (over-)analizing the whole Genki Dama thing is similar to (over-)analizing characters physical feats by using real-world physics. Toriyama didn't think things this way, and we are not supposed to think things this way. This isn't simple math + in-universe rules like with the BP calculations. In this situation, the things are just like this: Gohan's & co. genki is big because of quality, while the Earthlings', etc genki is big because of quantity. Together, they kill Boo.
Do you have any proof of that? There's nothing like that in the manga. We're only told that Gohan and co's genki is probably not enough to kill Buu, and that it is enough when combined with the genki of a few billion Earthlings. Meaning Gohan's genki < Pure Buu's full power. We know that genki is part of ki, so when combined with the fact that the Earthlings were enough to boost the Genki-Dama to "wipe out Pure Buu" levels, it's impossible for Gohan to be tens of times stronger than Buu.
But I suppose that Toriyama was thinking of things in terms of multipliers, right? This is a rather lame attempt to ignore evidence that runs contradictory to your power level placements.
Only if you don't want Boo suppressed.
It's not a matter of wanting. Nothing supports that, and the scenes he's in make substantially less sense if he is.