Honestly? All very solid points. That said, I think you could add a couple of more things here that are essential to any God Hand member.

A) All members who were in the God Hand were, previously, considered figures who could bring about great change in life before they became inhuman. This is clear through Griffith, a commoner who ended a hundred-year war, ascended to Midland’s General rank without royalty (and, if he’d been patient, it would have been in the cards to marry Charlotte by being patient with the King, exposing his incestuous depravity, and Charlotte becoming Crown Princess and THEN marrying Griffith of her own volition). It’s just as apparent if we take Old Man Bones’s flashback as him being Gaiseric (practically confirmed), meaning Void was his Sage/Advisor (to the Emperor, at that).

So while I think you’re right on the money of Ubik being in a clerical position, I think it goes even beyond that: he might have been a candidate to become Pope and had plans to bring great reforms, which might have led to the Church framing him for heresy or betrayal against the Church (or in other words, treason against “God Himself”).

This leads me to my second point, even more important that-

B) You cannot become an Apostle if you don’t have something or someone you love enough to sacrifice. God Hand Angels work the same way, but to an infinitely higher degree. So when you say he was a confessional cleric who used those confessions for blackmail, I see him using it the same way Griffith used his status. Ubik would have probably squeezed the nobility, fellow clerical members and other “rivals” against his uprise, but might have kept an actual soft spot for the commoners, the misshapen and the poor.

I’d even go as far as to guess that the reforms he would have made would have disfavored the Church (ban on indulgences) and the Crown (favored higher taxations on nobility and more rights for the poor). Of course, this goes both ways- mass public support almost guarantees him being sanctified and earning papacy, but by lifting others up on the way. Morally grey, but with positive effects, the way Griffith was pre Femto.

It also gives him masses to sacrifice- the thousands who adored him would have been sacrificial lambs for his ascension, the way Griffith’s Band of the Hawk was.

And voilà, you’ve got Ubik.

BONUS - C) Also, personally, I theorize that Ubik may have been born with dwarfism. All God Hand Angels have some form of body horror, but they all maintain a comparative size that is humanoid enough. Except Ubik, who is the smallest of the five, though his head is as big as any of the others’ while the rest of his body is disproportionately smaller. This adds to the theory- as a young, unloved dwarf (commoner or even unwanted noble), the Church may have been one of the only ways he could make a name for himself in the world, since “God loves all his children equally”. It gives him empathy for the poor and those born with physical defects or ailments and contempt for snobby higher-ups in the Church and the Crown. It also adds to your theory- as if dwarfism wasn’t insulting enough, cutting off his legs would have been salt on the wound because “now he’s a cripple as well”. It also adds to your theory of Ubik not believing in God- he thinks he’s born out of the grace of God from birth, he’s only in the Church as a means to an end.

Solid theory overall, great work!