Every class is hard and every class is easy. No class in this game has ever had a rotation that is particularly difficult to learn or pull off. Different players have different strengths and different weaknesses. I spent 2 hours on my friends 311 SAM and was able to get top DPS on a susano EX by a decent margin in that time. I do however find it to be tedious to play. In 3.0 I found Dragoon to be the most difficult class to play simply because keeping blood of the dragon up felt more difficult then greased lightning or Huton, I could play all 3. I just personally found the mechanics on dragoon more difficult, many people disagreed with me and that's fine. Most difficulty discussions are subjective to the extreme especially in this game. There isn't really a quantifiable way to measure difficulty.

At the end of the day every classes skill cap will be higher then most of the people playing them reach so it doesn't really matter. A top 10% player of what ever the "easiest" class is will be miles above the an okay player on what ever the "hardest" is.