That power runs out after a while and it shows no proof of omnipotence or limitless power, and tapping into omnipotent essence might give him a big boost it it wouldn't make him omnipotent. In reality Future Goku vs Superman Prime debate is just hypothesis and it can't be proven which side would actually win because of it. I prefer to stick to the non-future version of the characters, but everyone always ends up bringing out one or the other which results in this paradox.