SS3 Gokuu, SS3 Vegeeta, SS3 Gotenks, and Ultimate Gohan should've fought Pure Boo.

[Scott]

All at the same time. Make Pure Boo so strong that he stomps all of them. Bam, now it would be clear beyond a shadow of doubt Pure Boo is the strongest Boo and the strongest villain of the whole manga.

Vegeeta would've unlocked SS3 by training in the afterlife before Enma sent him to fight Boo.

 

[Scott]

 

[Spiral-Force]

What happens after they get stomped?

Tables turned with drastically low energy, Movie 8-style?