>>5478720>he'd want to have one "model" of Son instead of two competing versionsYeah. Can't forget that prior to his discovery, he had already developed variants of geneseed and even the Magnificat. A geneseed unique to our Acillians that no astartes has.
In theory, our Acillians could be capable of even more muscular growth and size than their astartes counterparts. Though, it's less evident they probably just build bigger size bionics and prosthetics anyway.
Consider that there are Iron Hands Primaris who just decide to robotify their bodies like the rest of their bretheren. They just build Primaris scaled bionics and replace their flesh with it. Even the skulls. (there's mention that some Iron Hands don't take off their helmets to reveal their face, because their helmet has become their face). But nothing stops us from doing that right now to both our Acillians and our Astartes.
I can just imagine the look on Fulgrim's face when he fought us, seeing our Steel Wardens standing a foot taller than his Pheonix Guard.