It was theorized that he would have had a bounty of something like 500m, and his powers were and still are quite incredible. His fruit alone makes him extremely powerful, his speed alone would be something everyone would have trouble with, and then the size of his attacks and the fact that they are electricity would add to that quite a bit. Add to that that he basically created a storm when he was fighting, and his attacks were absolutely incredible looking (Both displayed of his overall power), and you have someone that could have had their own during the war easily in my opinion.

Luffy being immune to him (completely illogical) was needed because the writers needed him to be beaten by Luffy, and it was before Haki was introduced so they needed some way for him to be hit (just like the ridiculousness with Crocodile.)

He wasn't my favorite villain, simply because it was VERY hard for me to get over the stupid rubber bullshit, but his power is the one I would choose if I could. Without Luffy being immune (I hate that nonsense) I would say he has one of the strongest fruits there is. It would probably take someone not very powerful or with much haki and skyrocket them to the 100m+ range of bounty abilities easily.

I really wish they had the foresight to not have Luffy beat Crocodile and Enel. He could have easily beaten both of them without a physical fight to the finish, and it would have left Crocodile having almost killed Luffy, proving he was far stronger than Luffy, and left Enel as someone who was so strong that they couldn't even fight him physically or take one of his attacks, but having beaten Crocodile in a roundabout way leads them to find one for Enel too, showing their ingenuity and abilities outside of just straight up punching people.

Crocodile was beaten when they stopped the revolution and united the country again, and Enel gave up on Sky island and I would have liked to see them stop him from destroying the place and maybe disabling his ship somehow and sending him off as his finish.

I probably agree with you on his placement in the scheme of things. I think being on Sky island and not knowing what Haki was (Obviously due to the early introduction before Oda even thought of Haki) is what keeps him in that position though. If he was in the blue sea, and had the 500m bounty like they said, he would know all about haki and that gap there between what we saw/got and what would have had him facing off against Admirals would have been a lot smaller. I personally believe that given the storm that he created, he had the ability to change the landscape around him like Aokiji and Akainu did, meaning he was probably pretty close, or at least "awakened."