It's about the whole moon stuff. It's definitely going to play a role in the future. Enel is still very relevant IMO.
Ehh that stuff was so important it was mostly relegated to cover pages. But if that's how you see it then fair enough.
However I don't think Enel altered the plot when it was his time on screen atleast. I think you're letting the fact that Lucci was only a lowly CP9 member ontop of not being the boss, blind you a bit. Idk if you misworded it but you can argue Lucci impacted/altered the plot and the strawhats specifically, more than any preskip villain.
And even if you want to talk about significance in universe, Lucci was being wanked by buster call VAs, strongest tobbi roppo (4th in Yonkou underling pecking order), and is the WGs leading fighting figure. Enel doesn't even exist, nobody cares or knows about him. You can almost argue he's filler.
Besides Enel coming back is only a possibility. Lucci has been back for a long time now, in movies and canon.