Listen, goku fought fatbuu and kidbuu in ssj3 form. Anyone can see kidbuu made his life miserable while fatbuu did not. Besides, the fight - good bu vs evil buu - should not be compared to any other imo. Now, as that video says, when buu absorbs he gets stronger, yet, he tends to calm down, wich means that, kidbuu might represent a higher danger i guess.
well now that I saw that video I see the differences between kidbuu - evilbuu like this:
Kid buu is more evil and wont calm down in a fight.
Superbuu has more power but is racionality would make him loose a fight that kidbuu wouldnt loose. I mean, cmon, trunks says "buu please stop, the fight cant beggin now, I must first fusion with goten ok?" and buu just waits. If he was kidbuu he would've blasted them before they even have fusioned.