I'm guessing that the previous art goes White at its' Mastery skill, and that it probably doesn't do any scaling after Mastery. I'm also guessing that it will go Gray not long after you get the upgrade. That would account for the 20 skill points (i.e 4 levels), since at 208 (20 points above Mastery) it was still green.
See my post right above yours (probably as you were writing yours). I agree that they should be better upgrades.
Kend
31 Brigand
Black Talons
Najena server
Brigand Combat Arts upgrade paths (shared timers)