It is absurd to think that one side has superior players than the other. Be aware of the steps involved in selecting either side. There is nothing that can stop someone from choosing one or the other side.
There are three main differences between a horde-based and an alliance player in terms of population, racial skills, and paladin/shaman. PVP is more popular with players who would rather play with the meta faction (horde). However, this is only an issue in comparison to the vast imbalance of population and the issues it creates.
My guild in 04 was rerolled to Alliance since Paladins were more powerful than Shaman and we were a PvE raiding guild. Because there were fewer players from the Horde side at the time of launch the guild was also more difficult to acquire quality Recuits. It had nothing to do with do with racial skills for PvE.
I'm not sure most players made up their minds to make a FACTION due to racial issues in vanilla. This wasn't the exact situation I experienced when I was younger. The Rank 1 friend I played with for a time decided to go with Tauren because the thought that they were cool.
No one said entirely this, but it's certainly not an accident the factions started out and ended up in the manner they were...easily explained earlier. I'm not going pretend that it's just a matter of people wanting to play with their friends, that's ridiculous.
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