In a game where we're expected to level several classes, this curve is a bit steep.
That's my main complaint about the leveling speed as well.
If we were only playing a single class, than it would be understandable. But leveling up a single class takes longer than in many other pay-to-play MMO's, yet we're expected to not just level a single class, but to mix and match skills from multiple classes.
If it were up to me, all mobs would come with a base amount of SP. If you kill the mob, you get that base SP. It's just like XP, it is guaranteed. Then you can earn additional SP through your actions in the fight, but not like right now. Right now SP gains are completely random and plain stupid.
I can get better SP from killing a weakling mob that dies in 30seconds than I do from soloing a mob 5+ ranks above me that take several minutes to kill. That makes zero sense.
Earlier today I was killing some yellow enemies and getting between 150-250SP each one. They died very fast, and had virtually no chance of killing me. Then I got into a group where we were fighting mobs a full 10 ranks above us, and my SP gain took a total nosedive. Why would I not gain more skill from fighting more difficult enemies? I'm not talking about over time, I'm talking about each individual fight. It's like SE has diminishing SP gains the higher the enemy you're killing.