TOAA is the creator of the omniverse, what do you want more ?
Basically, the definition of "omniverse" changes depending on who is writing this. Marvel qualified it as a "
Group of alternate universes which encompasses all reality" =>
http://imgur.com/z3gSlzc
Another definition:
http://imgur.com/Ab3Qq2f "
The Omniverse is the collection of every single universes, dimension, etc. Everything is in the Omnverse, and there is one Omniverse."
Another one:
http://imgur.com/a/uN6eX "
The Omniverse is the collection of every single universe, multiverse, megaverse, dimension (alternate or pocket) and realm. This includes not only Marvel Comics, but also DC Comics, Image, Dark Horse, Archie, Harvey, and every universe ever mentioned or seen (and an infinite amount never mentioned or seen) including our own world. Everything is in the Omniverse, and there is only one Omniverse. According to the Official Handbook of the Marvel Universe: Alternate Universes, "It includes every single literary, television show, movie, urban legend, universe, realm, etc. ever. It includes everyone from Popeye to Rocky Balboa to Ronald Reagan to Romeo and Juliet to Luke Skywalker to Snoopy to Jay and Silent Bob, etc." This includes universes outside of comics, such as Star Wars, Dragon Ball Z, Hunger Games and Assassin's Creed. The Omniverse is EVERY reality, including those published by all other companies. Even fan-fictions, cancelled works, mere fantasies, wishes of thoughts created by people, and fictional universes yet to be published are considered part of the Omniverse, simply put the Omniverse is every version of reality and existence imaginable."
TOAA is "the entity believed to be the supreme being
creator of the Omniverse" =>
http://imgur.com/z3gSlzc
TOAA didn't appeared only with Peter Parker to eat some sandwitches. It wa stated that the Heart of the Universe is TOAA's fragment of power:
http://imgur.com/Pbmpak0 With the Heart of the Universe, he became "God" and omnipotent/omniscient/omnipresent, and he's still below TOAA because it was a fragment of TOAA's power, Thanos was "manipulated" by TOAA through this time.
TOAA gave to Adam Warlock the role of the Living Tribunal, an omniversal entity:
http://imgur.com/z31CcSW . The One Above All isn't featless as many think. It doesn't mean that those events were not canon that it wouldn't be taken into account. TOAA is beyond all realities and dimensions, it includes non-canon stories, there is only one TOAA.
Thanos with HOTU controled the entire omniverse
http://imgur.com/Ye6ecDk, he absorbed the LT, Eternity and Infinity
http://imgur.com/JSIG8lu and became God, but Thanos said himself that there was still a superior force he could not absorb, he clearly mentionned TOAA who manipulated him.
http://imgur.com/c1Ldrjz TOAA > Thanos HOTU > Omniverse.
TOAA is known as the only entity above the Living Tribunal
http://imgur.com/V17hw16, LT who is on an omniversal range:
http://imgur.com/dMzkFKg The spectre know the Living Tribunal, The Brothers know the LT:
http://imgur.com/RbnPHCE and
http://imgur.com/UesEotJ
Many statements confirmed TOAA's omnipotence:
http://imgur.com/yNZPG39 and
http://imgur.com/XROO0mq The fact that TOAA is supposed to be "God", there's no reason why he couldn't be omnipotent, he represents Yahweh and the True God in all religions.
Pre-Retcon Beyonder is supposed to be "God before there was genesis", the Beyonder is known as to be omnipotent, so is TOAA.