Okay okay, didn't explain it right
An object/property/characteristic is defined by what it is, and what it is not. being omni-anything implies that it encompasses all that what that trait has, and all that it does not. For example an omni-island would contain all that defines an island and all that doesn't, so it would be the absolutely most perfect island of all time, but it would be completely under-water and then not be an island at all.
infinitely powerful would be closer to what you're explaining, omnipowerful encompasses all levels of power at the same time, from a be all end all ultimate power, to a complete and utter lack of power, to being essentially a power sponge absorbing the power you do not have, and everything in between, possesing all this at once would result in an essential neutrality.
infini means the ultimate expression of the descriptor, omni means every expression of the descriptor