I don't think Reiner's arguments matter too much at this point (the whole No Watch Ben's future changing stuff), so here are my arguments:
Eon says that No Watch Ben's
timeline doesn't have an Omnitrix, not just the present moment:
Eon: Yours is the only
timeline without an Omnitrix,
which makes it an unpredictable
wild card.
Vilgax: And in my future,
there is no room for wild cards.
When Paradox talks about alternate timelines existing he'll always mention the point where said timelines branch from the Prime timeline:
"Paradox: As Gwen guessed, cross-time is made up of parallel versions of the history we know. There are hundreds of them... a world where Gwen found the Omnitrix, a world where albedo turned to alien x and was trapped motionless for nearly a year, a world where you didn't have to destroy the Omnitrix to defeat Vilgax. Ben 10K: Et cetera. Paradox: Ad infinitum."
Meaning that the following statement:
Amazing- a universe without an Omnitrix. It boggles the mind.
should refer to the point where No Watch Ben's timeline branched from Ben Prime's timeline, meaning said timeline never had an Omnitrix.
Lastly if the Omnitrix did exist in the past of the No Watch Ben timeline at one point, it would have been pretty easy for someone to get this Omnitrix and give it to No Watch Ben or Max. Even without accounting for Paradox, there
exists tech which allows time travel (yes these comics are accepted as canon) as well as spells for it. Making Vilgax's plan very flawed, which it shouldn't be.