Idea: The Matrix, being a parasite that uses the Primes as it’s hosts, slowly turns the Primes into eldritch horror-ific beings, and the forms they hold in front of people to make them appear normal are actually just a ‘cloaked’ form for their ‘true’ form (Maccadam from CV for example). This happens to all the Primes, it just usually takes a long time even by their standards to build up enough, and usually the newer/younger ones are like baby horrors.

Another idea: Rodimus, having been born in the primacy essentially as Optimus’s son, has grown up with them, and seen them in their true forms from a young age. It is now impossible to freak him out with them, because before Hot Rod could walk, he looked Nova dead in the face in it’s true form as it cradled him in it’s arms, and cooed up at it. Optimus now says that to Rodimus, they’re not horrors, they’re eldritch wonders. He genuinely looks at them and believes some to be quite pretty. Or he calmly/casually asks if Op thinks Quintus’s Subnautica octopus ass could fit in a flower vase, because octopuses don’t have bones, and this is long dead ghost, so it’s gotta be possible, right? (Op just wants one normal conversation about the Primes with his son. one. that’s all he asks (while snorting laughs but that’s beside the point-).)

In short: The Primes are eldritch horrors in their true forms + Rodimus isn’t bothered in the slightest about this fact.