1. The book was not one of C. S. Lewis' better books, so I actually agree with Orwell. If you're going to be explicitly Christian, be Christian. But, he sort of got into the Space Occult. Like, it was too ambiguous... I think that's what Orwell was trying to say, is he didn't come off as Christian--which is ]h]is prevailing ethos--and it disappointed it, when it ended without a discussion, as I was expecting Merlin and the Head to dialogue, rather than just end in a Deux Ex Machina.

2. I think working from the framework, if your story incorporates miracles, you have to be cognizant of the ethos you're working through. Which, Orwell probably wanted a Christian moral, and when he didn't get it, the book was confused, and it began to be kind of schizophrenic. I'd say that was my problem with the book, was it didn't work from a Christian framework, but rather was a sort of unbelievable space occult thing, which Narnia is leaps and bounds better, and so are Lewis' essay works. The Space Trilogy was always low on the totem pole for me, on Lewis' corpus, and I never really did like it. But, miracles don't depreciate the stories value, but I think the invention of a Mythology and mixing the Occult with Science, that's kind of disturbing--and may be the actual strength of the novel, I haven't figured that out. But, I found it kind of eerie, and I didn't get the respite of a Christian message. Which I think might be Orwell's problem with it, all around, is it didn't stick to Lewis' ethos, but rather diverted off of it, into occult magic and stuff like that.

3. I'd say the answer is not different. It's just you got to choose your ethos. And Lewis' ethos is Christianity. And this was a particularly early work, but he was also writing Mere Christianity at this time, he should have known better. I felt kind of alienated from it, as I couldn't implant Christianity into it, but rather it devolved into its own mythology. Which is something people do today--so it's probably more readily accepted today, with the culture's general malaise toward Christianity, you have mythologies like DBZ and Japanese Anime making Gods and stuff, where DBZ kind of lost my interest when it transitioned from an Atheistic world to a Theistic world, and I think the problem here is the same. Putting Gods and Goddesses in your work kind of warps it. Which, you can say Aslan is sort of like that, but he's more of a symbol rather than a literal. Where I think the problem with The Space Trilogy was it was literal... and that's not God's name, so it sort of offended Orwell, who's, although unwillingly, in that Christian society that wants real Christianity, or none at all. Like is said to Laodicea. 

https://apilgriminnarnia.com/2020/09/10/george-orwells-review-of-c-s-lewis-that-hideous-strength-throwback-thursday/

I had just understood, that the area of a circle formula is like Length times Width. But, hold on... a Radius is not the same thing as length. So, you do the same math expression for a rectangle, it will not work, but you do it for a square, it will. Because half the parameter of a square times its radius would equal the area. So this math works for a square, because it is equal, the same that it works for a circle, because it is equal. However, said area formula will not work for a rectangle. Because a rectangle's side lengths are not equal.

It is because of this, and is also the same that Quintic Roots cannot always be solved, that the P versus NP cannot always have a solution, and only some Quintic Roots can be solved. Because solving it would generalize a universal formula for all shapes, which is impossible.

However, many are not unsolvable. One can take known principles of geometry, and combine them like a Geometric Proof, and solve many NP difficult equations, if one graphs the shape and breaks it down into its composite parts. Like in a Geometric Proof.