Technically speaking, there are two starting zones--Howling Mountains for Humans, and Elven Island for the Elves. After all, a new character can start only in one of those two zones. Elvish characters have a distinct advantage, since they can level their starting class on Elven Island, transport to Varanas to pick up their second class, then travel to Pioneers Village and Logar in order to level up that class and pick up the first of the Epic quest lines. Humans can only get to Elven Island by way of a kindly Elvish character marking a transport spot somewhere on Elven Island and opening a portal to that spot for their Human friends.
Sacsilia Steppes was originally conceived as a "continuation" new zone, specifically for leveling a Human character's newly-acquired second class, along with quest progressions leading into Dragonfang Ridge and its quests and instances.
Coast of Opportunity was and is intended to be yet another "continuation" zone, for any character's newly-acquired third class. It, and the companion zone, Xaviera, were designed for the rapid advancement of that third class, so that a player will essentially spend a minimal amount of time getting their third class to match (or close to it, in a number of cases) their other two existing classes. Remember that when those zones were introduced at the start of Chapter IV, 95%+ of the characters going there were already established, many of those already being at or near the previous level cap (level 65). Any character, established or relatively new, can gain access to these two zones by leveling to 20/20 and then visiting with Johnny Dutin in the Hall of the Eye of Wisdom in Varanas. Discussion of whether or not this is a Good Thing would be considered to be well off-topic. Just saying.