I think that 5v5 is ideal, because it provides a good balance between ability usage and combat worth. With five fighters, you can afford to, say, roster someone like Fina with zero combat worth but an excellent start of battle ability. With only three fighters, those kind of tactics just aren't viable. So it cuts down on strategic choices.
Obscurity is a much bigger problem for casual votes. Even in a 3v3 situation, if it's like Garner/Tawodi/Hibana vs. Geddoe and Varik in X-D "Dragoon," casuals are going to look at that and leave. By contrast, if you have even M1-sized teams but Sephiroth and Trance Kuja and Mega Man are the headline mercs, casuals can get a handle on that.
This isn't to say that I personally could do better in terms of build creation. Maybe 24 teams is too large (too heavy?) to sustain a decent-sized release pool of well-known fighters.
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You put your RESOLVE HAT back on, which conveniently is the same hat as your NORMAL HAT.
{Drakeryn}