I wondered the same thing when comparing my Dark Warrior and Turtle. My turtle could have obviously better items and be higher level but my Namekian was at a higher power level.
I found out it's just the HP and DEF difference between the two. It's not his gear, although that does play a part.
Defense is still broken, so it's not like he is actually using that strength.
Namekians will always have 2-3 times more HP which means their power level even in the same exact gear will always be larger.
You get better by upgrading skills, buying items and upgrading them, and performing how your class was meant to be played as accurate as possible. Don't really look at power level compared to others because their are still features that affect it that aren't useable right now.