> NATO is not just about Russia.
Not only, but for the most part....It's about Russia.
> Turkey brings a military ~30x the size of Sweden
On the other hand Sweden and Finland at 2% GDP has a similar defense budget to Turkey. Money does not a military make, but "30x the size" is only counting manpower and not much else. Modern fighter aircraft is around a factor 2x rather than 30x, for example.
> a buffer for conflicts in the Middle East
> advanced military manufacturing capability
> partnerships with affiliates throughout MENA
These are all very important.
> "soft" cultural, christian, western centrism (calling things racism is taboo on HN so I will refrain).
It's perhaps easier to look at democracy and press-freedom indices then, to see why Turkey isn't like the others. Perhaps that's what you meant? The problem is that undemocratic/authoritarian states tend to be stable, until they suddenly aren't. NATO is supposed to be a partnership of democracies (It's a prerequisite for applying!) so it's safe to say that being not-a-democracy isn't popular once in the alliance either.
So sure, NATO is a defense mechanism for what some would call western (that is: secular, liberal, ...) democracy. That indeed does touch on culture and religion, but only superficially. Turkey has long been the champion of secularism in the area, and obviosuly everyone in NATO (and elsewhere) hopes that will remain the case, hence one is reluctant to push Turkey away too.