I can only go by experience in FFXI, but it was effing hard to get ppl together for 18 man bosses, granted stuff like Panda and Abso Virtue took HOURS to beat, I think the 8 man solution is great for this type of game, as we see in CT, 24 man stuff is just button mashing the HP to zero, most times ignoring many mechanics. Orchestrating some of the challenging and exciting Coil mechanics would be a pain to formulate for 24 ppl, and Coil would be crap if it was a "stand there and button mash your combo till boss hits 0%" like other popular MMOs.