Hey,
I've seen different version of your idea and I have never liked it when I have joined new servers.
I've seen server's where you had to practice using moves to unlock the next move. Having a bending rank that gets higher and unlocks more the more you fight.
Also, you could say McMMO's 'unarmed' is a version of this idea, since it does the same thing in a way (increased damage)
The reasons I've left these server's as soon as I've joined them are as follows;
If I'm looking for a new bending server to join, I will be trying quite a few out. I like to jump straight into the game, head to arena and fight.
If you limit my moves forcing me to rank up to use them, I can't test all of your moves to see if I like how you've edited them, or to see if they're balanced.
If people who play a lot do more damage, it's an infuriating grind in arena against player's who do more damage. I just have to die lots of times whilst ranking up my moves for more damage in the arena, which is NOT fun.
I think what would be more a more user friendly version of your idea is;
Give them all the moves that you usually get at all the same damage.
Have a way for them to rank up after a while to have access to added moves OR different versions of the moves you already have.
For example- When they first join they have normal firejet. After they rank up they gain access to FireJet+
-Loony