Maybe it's my lack of a freudian mind, but am I the only one not seeing these ships as vaginas?
My initial reaction to both was that they had an aesthetic of looking like something the Advent would worship, if you will.
The Coronata looking like an obelisk or pillar, or an idol embodying something or someone, think how people pray at statues of Mary. The Eradica was designed to look like angelic (the thing was originally named Cherubim for christ's sake), more so now that they've swept the "legs" back.
Both fit the faction's principles, the Loyalists are about forcing people into their cause, like people would flock to an "idol" to worship, whilst the Rebels are about death, rebirth, renewal and redemption, their Titan uses it's followers to heal itself and grows more powerful if something kills them, it's a guardian angel.
Or maybe I'm reading too deeply into it and you're all right and the art team were clearly trying to design giant space vaginas, I don't know.
(No really I don't even get how the Rebel one of all things looks anything remotely like a vagina.)
Edit - Also I feel like the only person who likes the Eradica's floating disk thingie. Can't wait to see the functionality it has, since we know the Coronata's halo fires giant lasers.