FWIW, this has always been my take on the trilogy also. I reread it within the last two years and my take was unchanged. Part of the problem with Perelandra is that the story just bogs down in the middle, and like you say, the premise is just missing a few nuts or bolts and isn’t enough to carry the story through the slow points.
That Hideous Strength is creepily prescient, as is The Abolition of Man. Lewis was able to see a flaw in science-as-worldview, I think, that’s grown significantly in reach this century and really metastasized during Covid. With 9/11, people were interested in questions of evil that science-as-worldview really can’t address. But Covid seems almost tailor-made for the Belbury crowd.