(psst, you forgot DHs)So, basically, you're proving his point.
The Alliance has 5 races that can be paladins while the Horde only has 2 but the Horde has 6 races that can be shamans while the Alliance only has 3, is the same difference of 3 races in both cases. As originally paladins were Alliance only and Shaman Horde only, I do not see any problem in how things are at the moment, but I believe that if the Zandalari got paladins the Kul Tirans will receive shamans to keep the balance.
Interesting fact, ignoring Kul Tirans and Zandalari that we are still not sure of the classes that they can be and Pandaren that is equal for both sides, follows a list of combos between race and class currently existing within the game:
Equal on both sides:
Hunter - A = 9 / H = 9
Rogue - A = 7 / H = 7
Warlock - A = 6 / H = 6
Warrior - A = 9 / H = 9
DK - A = 6 / H = 6
Allaince have more:
Mage - A = 9 / H = 7
Paladin - A = 5 / H = 2
Priest - A = 9 / H = 7
Horde have more:
Druid - A = 2 / H = 3
Shaman - A = 3 / H = 6
Monk - A = 7 / H = 8