Ulysses HQ is in the real world though. But yeah I agree the father son would be too cliché.I feel like it's more likely that Orion and the Founder met at one point in Eternum when the former was a kid, likely from a bleeding effect moment that he forgot (when his powers were still in its infancy).
As to where he got his powers, it could be from his mother side instead if we go by your theory. I just don't think Cari would be lazy enough to repeat the same twist that he pulled in OIAL, so I'm leaning on the idea that his dad is really his dad, and that there's probably a reason why he's so distant to his own son (maybe he just didn't appreciate being a single dad, or maybe he loved Orion's mom very much and the separation still pains him that he keeps his distance from his own son because he reminds him of her...there's a lot of possibilities regardless).
But if his origins are something bigger, then his earth dad definitely isn’t his real dad.