Do we really need 50 playable factions? I've been playing M2TW more or less continuously since January 2007 and by my count I've only managed campaigns as 12 different vanilla factions, and several of those were short campaigns I got bored of and gave up on. Having 50 fully playable factions complete with voices, videos and battle speeches would mean I would likely never even use around 4/5ths of the content of the game by the time the expansion, the first big mod or even the next game comes out.
I'd certainly rather have 12 very well balanced and polished factions with another 38 basically playable but a bit more rough around the edges, than 50 virtually identical factions with generic units, differentiated only by a different colour scheme. And if I saw a game advertising itself as having "50 playable factions!" I would probably think "too good to be true, what corners did they have to cut to get that many?"
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