I don't understand how you can even argue with that, changing class is nothing more than creating a new char without losing progress why should that be even more expensive than a server transfer
I can argue with that because I have come across some potential difficulties in my envisioning of how class-changing could and would work and that's about it.
Having read your response, I think we both look differently at the game. According to you, "changing class is nothing more than creating a new char without losing progress [...]". Although that simile is wrong, I get what you're trying to say. But here's where I see things differently: creating a new char with a new class does not result in losing progress - you still keep your progress, just on another char.
To point 3: you wrote that "[...] your grind is over, you can just play the game for fun [...]." I perceive TERA as a game I mostly play for fun, including its grind, so all I do in TERA is for fun. In my perception, once I've reached everything I want (including 2.0, fully enchanted accessories, HO +3, relics etc.) it's up to me to either quit the game, continue with my fully developed char and class start a new char or class from scratch (which would be the most fun for me), or to change my class in case class-changers will get implemented.
Once again, do not get me wrong: class changers would be a huge deal and I would happy for you if they actually made them, but I doubt they will be implemented. All I did was to voice my thoughts about that.