Prots cannot be kited once they land their first stun on their target. 2 ranged stuns give them sufficient time to pin the target and catch up.
Warriors enjoy kiters; it gives them distance to assault. Roar is a spammable and sustainable slow. Its cooldown is not 45s.
Assassin have deadly chaser, a slow that only lasts 9 seconds, and has a 45s cooldown. It is not spammable or sustainable. The 40% speed reduction still allow the target to move at such a speed that the assassin must spend a short amount of time moving between hits, thus reducing effective DPS.