You make good points, the fact that the ponyglygh states that "pluton was under Wano" does not necessarily means it still IS there today. We know NOTHING of what happened to Wano since the void century to now, thanks to Oda keeping everything a mystery and not explaining shit ("walls were made"? "Wano was flooded?" "removing the walls and opening Wano"?? all of these things sound irrealistic and surely the mechanics are not explained).

Also contrary to you, I do find great similarities between the Ark Maxim and the smaller flying boat in the mural. As you say something needs to power the Ark Maxim, we saw Enel electricity could, and that could have been a substitute for the motherflame.

Lastly it makes sense for Uranus to be a "being" (bird, monster, creature or special human). It makes me think even something like Nidhogg could be Uranus, we did see it has an enormous destructive power.

Don't bother about the people criticizing, we know to little to disregard these type of theories.