The skill comments are misleading, theres more information on the link at the bottom but here's the general gist of it:
KFCrispy said: The A+ skills require a lot more SP than other skills ("Slow" requires 1410 total SP to reach A+... "Genius" requires 1130 SP to get to S, "Excellent" requires 670 SP to get A)
the opposite is also true - there are a few skills character easily can learn but instead of reaching A or S, they stop at B+ ("Fast" learners only need 435 SP to reach B+ vs the normal "Good" B+ needing 549 SP).... so they learn/train easily but simply don't have a high potential. Ace's Swing skill is one of these Fast learner skills.
http://suikosource.com/phpBB3/viewtopic ... 10&t=11813