CO2 is going to be neutral for the peels. You're just transporting it from where the oranges grew to where they were dumped. The CO2 benefit is purely from the trees and other biomass that grow where they wouldn't be growing before.

As for methane, that's a good question. Orange peels are better than most things because the limonene inhibits methane producing bacteria. But you'd still get quite a bit in the deeper piles (that produce the anaerobic conditions needed for methane production).

Spreading them out more would help, but might interfere with the beneficial effects.

I may be wrong but isnt most of the tree carbon capture over stated as in the overwhelming majority comes from algae in the oceans?

While forests are great they are not the best focus iirc compared to the oceans.