[@thewizardguy] I'm pretty sure the omniscient part relies on his lightning enhancement. Otherwise yes he's very skilled at it. 

Considering how powerful Luffy's haki was in gear Fourth, highly unlikely. It's based on power levels and the power of friendship, but Haki is indeed a hard counter to exaggerated Logia types. He did defeat a guy who could turn anything into strings and had exceptionally powerful Haki. 

Yes, except those that are relevant like any important crew member in a Yonko ship. Or an Admiral. Though to be fair it's impossible to judge as a lot of these depend on hype. Kizaru barely displayed how his abilities truly work, Kuzan is strong but seemed like the underdog and Akainu while his ability isn't super original is kind of the Big Cheese for a reason. Fujitora I don't know, he never displayed much of his gravity powers. 

Is Enel one of the strongest? Hell yes. Is it sound to claim he'd beat most people? No, especially when Doflamingo put the bar so very high and he's not even the last War lord to be showcased. Because of Haki I'd say Doflamingo defeats current Enel. But that'd be extreme difficulty.