Note that Gosen Zosama says Base Gokuhan would not need to transform to beat Bootenks:
Base Gokuhan >= Bootenks
El Manga Legendario implies that the "Rival Boost" makes up for the difference in Vegeta & Gohan & then some, leading to Vegetto surpassing the hypothetical Gokuhan:
Base Vegetto > Gokuhan
Bootenks (absorbed Piccolo & Gotenks, who both have extensive knowledge of the Metamoran Fusion Dance) concludes that a hypothetical (most likely SSJ3) Metamoran Fusion of Goku & Gohan would be beatable:
Bootenks > SSJ3 "Gohaku"
Boohan senses Goku & Vegeta, & states that their merging (Metamoran Fusion, as it’s the only type he knows of) would lose:
He is most likely thinking of a SSJ3 Gogeta, because of his dealings with Gotenks. Boohan > SSJ3 Gogeta
There's also this, but, not sure about the validity of the source "Dragon Ball Kyogen 2".
So, Base Vegetto > Base Gokuhan > Bootenks > SSJ3 Gohaku >= SSJ3 Gogeta ~ Gohan
You can put Boohan where you like, but as you can see, Gohan < Base Vegetto.