Supporter is the opposite role to controller. Supporter buffs the party and protects it, the controller strikes with debuffs and suppression against the enemy.
The Leader is the opposite role to the Controller. Leaders dictate which actions might be beneficial to the party, the Controller dictates which actions might be a hinderence to the enemy.
The Controller has an ability to make difficult terrain. The Leader has an ability that allows characters to ignore difficult terrain.
I don't see the semantic problem.
Supporter is really so negative of a term that those who prefer playing supporter classes like the cleric and warlords have to have an ego boost by being called leader? Seriously?
It's a difference of action vs. reaction.
A supporter asks his friend what his friend wants to do, his friend says "I want to hit things!" the supporter makes him hit things harder.
A leader doesn't ask. A leader says "I think it'd be a good idea to hit things, have a bonus to that." The friend can then choose to hit things and get the bonus (like the leader asked) or not (presumably, he's got a better idea in mind, like drinking a healing potion or moving beyond the trap).
If I give you a +2 to saves vs. fear, am I a supporter, bolstering your defenses? Or am I a leader, telling you to stop sniveling and go face that dragon's aura, I don't care HOW paranoid you are.
It's the same thing, and "supporter" carries more "second class citizen" baggage. Active voice is better than passive voice. Acting is more fun than buffing.
Because when I think support, I think bras, and when I think leader, I think Alexander the Great.
Which do you think I'd rather play in a fantasy setting?