Kizaru is faster, enel can only move with a metal conductor, and Kizaru can light speed anywhere (not sure about Enel, but still, that's my opinion).

what I meant about him being over-powered, was that when we first saw Aoikoji, we saw that while being super strong and all, he was still "fighting" before going on overdrive with his fruit.
he first played around a bit, and when things got serious (Sanji-Zoro-Luffy team up is serious) he used his fruit abilities in a manner that isn't all about 'killing the enemy', the abilities he displayed, were support type to his fighting skills (ice blade, ice kawawimi, ice armor) and not weapons by themselves (light kick, light beam). it's a matter of feeling, not ration.

about the fruits: we've seen (enies Lobby) that the marines have many fruit user at the level of commander, and like Smoker (what's up with him lately?), they get promoted from time to time. I think that the fact that they're all Logia, is more of a 'story coincidence' rather than plot driven. I don't think there's any secret behind it.
if Dr.Vega could bring them fruits, I reckon he'd get the CP some better fruits, or at least earlier. could be, though, it should have taken a whole bunch of fruits to invent Zoan type swords...

as for ONE piece rocking the manga jungle...
Oda made his story an adventure, rather than action story, he doesn't apologize for making his characters stronger, or for making them actually climb from being the small fish in the puddle.
OP has been going on for 500 chapters, and they've only now gotten to the point that the Higher up notices their existence (along with 8 other, equally strong pirates). Bleach made Ichigo win against captains less than 150 chapters into the story, and Naruto was targeted by the super akatsuki ninjas as soon as chapter 150ish as well. so while Op can keep up with decent villains, who are just as petty and generally un-important as the ones in the first volumes, Naruto and Bleach have to keep inventing new freak enemies to fight, and make up some ridiculous back story to support it .