The Cosmic Trilogy is one of my favourite works of C.S. Lewis.
That Hideous Strength is the strangest of the three, but I still enjoyed it. Its depiction of evil is chilling yet so accurate. The very human longing to be part of the “Inner Ring” can lead people to commit acts of great cruelty.
I’m not sure if the OP has read through all of the book yet, so I will warn of potential spoilers in the rest of my post.
One of my favourite parts of the book is the descent of the gods (the planetary
eldila) onto St Anne’s. The description of these
eldila (especially the ones not encountered before such as Glundandra), is nothing short of breath-taking.

Yes, I’m glad I’m not the only person to be puzzled about this. Ransom tells Merlin that there are no longer any Christian princes left, but the whole time I kept thinking ”…but what about the Pope?” That exchange between Merlin and Ransom was frustrating to read as a result.
I agree with this as well. The story was masterfully written with so many rich themes but there is a definite Protestant bias to it.
There are other omissions of Catholic themes in the trilogy. For example, in* Perelandra*, Lewis goes to great lengths to compare Tinidril to Eve, and Tinidril is called “the New Eve”. The earthly Eve and her Venus equivalent are placed in opposition to each other, which makes sense given the* Paradise Lost *themes within the book. However, it’s curious that in this representation of the universe, there is no mention of Mary. This is odd given that one of her titles is actually “the New Eve”. I would have thought that would at least warrant a mention by one of the planetary
eldil, especially since they do reference Maleldil’s (i.e. Christ’s) incarnation.
In
That Hideous Strength, there is also discussion about the features of fallen, corrupted femininity and its heavenly counterpart (as represented by the earthly Venus and Perelandra respectively). But again, Mary is not mentioned at all.
At any rate, it would be interesting to see a Catholic commentary on these books. There is so much theological and thematic richness to them, though its avoidance of Catholic themes (Mariology, the papacy) is notable.