@sigfrid yea I think so to, because there's a lot of back story to still explain and yes you could put alot of background information in a tournament arc, but you can't put ALL of the backstory in the tournament.
Im assuming that purgatory will literally give the kengan association a run for it money and probably sweep them. I'm assuming purgatory has a higher skill pool (like fighters from the inside, the tiger vessel guy, and "Tiger" Niko).
I feel as they'll have another arc after this first tournament arc to settle it, and in that arc Koga will be built up to be more believable to compete with ryuki, ohma and the rest.
Some might say that ohma coming back is an ass-pull (which I don't believe, seeing as worm is developing as a major corner stone in the manga) but for Koga to magically compete with ohma and the rest as he is right now, is an even bigger ass-pull.
ohma, ryuki, gaolang, agito, 8th fang, nitoku, okubo, that judo guy, julius (?), wakatsuki, raian.
only 11 so far.
i'd expect sen going to fight for purgatory.