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In my opinion, when it comes to the number of factions, there are two paths... let's consider them with examples...
First: Games like Age of Wonders, with 12 factions in the first part, then 16+. The balance is non-existent, but people play it because of the variety, the partial uniqueness of each faction, and so on. Currently, the game is dead and only a few fans remember it...
Second: The game Starcraft - there are THREE factions. The balance is almost perfect, and the factions are ABSOLUTELY different. It participates in all esports competitions in the world. In Korea, it has become a religion. Even after NINE years since its release, it remains the BEST strategy game.
Personally, for me, balance and uniqueness are better than a multitude of pseudo-different factions.