Doesn't the combos change a bit for each variation? I did remember hearing "why because this baristions has the easier combos?" When they were showing off Ermac
Sometimes, but not usually. They said that about Mystic Ermac because his tele-slam holds them up for an easy combo. It doesn't do that in the other variations, hence less combo opportunities in those.
Here's Ermac, using him as an example to see how little the variations change from the moveset:
Master of Souls - Adds two moves: one projectile attack and the ability to instantly disappear and reappear at will. The projectile stuns the opponent if Ermac has three souls floating around him. Using the projectile drains the souls and you need to wait for them to recharge.
Mystic - Adds one move and changes another: He gets the Force Push, and his teleslam, which is universal, now keeps the opponent open. It's possible he gets some added normals, but we can't know that without knowing the whole moveset, which they didn't show.
Spectral - He loses one move, gets a new move: He can no longer float and do the groundslam. Instead, when you do that move, he flies in the air, where you can maneuver him and do special attacks only available in the air.
See, the difference from one variation to another is just a couple of moves, usually. But these moves generally change your strategy.