Simply put, fatigue was put in place to hide the fact that the game was lacking in content.
I can agree with you in some respects but I don't think that the fatigue system was put in solely for this reason.

More likely the team wanted players to create hybrid classes that could perform multiple class actions on a class (by leveling up another class). However, this has cost them as the horizontal development of characters restricts them from balancing the classes. Because of this sytem, people have leveled up multiple classes and imo this has destroyed the class identity as a class can use many skills from others.

If removal of the fatigue system means that classes can be balanced better and give them more of an identity, im all for it!