Back in the day (as recent as MOP tbh) I could always pick a class for the X.0 patch and be happy with that decision of the rest of the expansion until they made major changes for the next expansion.
Today I can't really be sure if my pick is going to last until the next patch until changes make me have to reconsider, I personally find it exhausting and demotivating not feeling like "this is my main and I'm gonna work on it for the next 2 years".
Should classes and specs be tampered with less over the course of an expansion?