The Last Battle is... pretty blatant in a lot of its issues, yeah. There's the part where the main villains are "those weird, dark-skinned turban wearing guys who live in the desert, also they're really cruel they take slaves and conquer people and stuff", and their main god is apparently the Satan analogue of the setting. There's the aforementioned part with the Dwarves where because they don't believe, they're shown blindly stumbling around the afterlife not actually believing they're in heaven but still in the shed or whatever everyone died in doing things like drinking from a river and saying "guys I found some water in this horse trough". There's the part where wrapping back to that Satan type guy, there's one Calormen (fucking hell I JUST got that thanks Lewis) who is a good dude despite worshiping that Actually Satan figure, so Aslan's all like "oh yeah anyone who does good deeds in the name of their false gods is actually praying to me don't worry bro". There's the part where Susan has apparently grown up into silly things like boys and makeup and "oh doesn't have time for that make believe land of Narnia anymore".
TL;DR - just stop reading the Narnia books after The Silver Chair. The Last Battle... really doesn't hold up when you come at it as an adult and can read between the lines, rest of the books aren't nearly so heavy handed or preachy from what I recall. Sure, there's some small level of "it's a book of it's time", Narnia series was written in the 1950s, but... boy howdy everything involving the Calormen alone.
Hold on. Why do you assume that "Calormen" means "Color Men" and not something like Spanish "
Calor (heat) Men"? Remember that they live in a
desert. In creating Calormene, Lewis did the kind of worldbuilding that we normally praise here: instead of directly copying any particular culture (usually poorly), he took bits and pieces from
many different cultures to create something new. Yes, they have some Ottoman features, but they also have Aztec features and a bunch of other stuff. (Never mind that the primary villain of most of TLB was Shift, a demagogue who happened to be an ape and wasn't even from the same cardinal direction relative to Narnia as Calormene.)
The fate of the Dwarves is literally Plato's Cave, and it's presented as a punishment for their attempt to
both-sides Literal Good vs. Literal Evil. ("The Dwarves are for the Dwarves!")
Within the context of a setting where Christianity is Absolutely Real, "as long as you're a good person you're cool" is just about the single best possible implementation. As an atheist, Aslanism is solidly within my realm of "ehh, I'll take it."
The whole Susan thing is just decades of misinformation taken as fact.
Pride and Materialism are what she was judged for... not that she could immediately join the others in Aslan's Country anyway, because
she was still alive. Kinda hard to enter Heaven in that condition, unless you're Enoch or Elijah (I guess). The whole mention was very possibly intended to be a sequel hook, but then Lewis died.
And because of how the series order works, "Stop after Silver Chair" can mean either "yes, read Horse and His Boy" (which is almost
entirely about Calormene) or "no, skip Magician's Nephew too." (Full disclosure: Horse and His Boy was always my favorite of the series, with Last Battle as either 2 or 3 depending on how I felt about Silver Chair at the time.)
