Is that a plothole? I wouldn't say #17 doing so is a plot hole because he was formely a biological being who was modified into a cyborg with infinite energy, but #8 seems to be entirely rebot, just like #16.
#8 doesn't know how the Genki-Dama works, not to mention we never saw his Genki leaving his body like with the guy 5 pages prior. For all we know, he was contributing nothing.