It's like saying you have the fastest integer math library ever written, with the minor caveat that it only supports numbers smaller than 256 because it achieves that speed by being simply a hardcoded lookup table, and crashes if you give it anything else.
Of the functions that take strings, the old ...A() versions should never be called anyway since they depend on the obsolete concept of code pages. The proper way to work with strings on Windows (IMHO) is to encode all string data to UTF-8, only encode/decode from/to UCS-2 when needed, and call the ...W() functions explicitely (don't use the global UNICODE define).
Also see: http://utf8everywhere.org/
And with case-insensitivity it gets worse, as there are some locale dependent additional rules, for Turkish and Lithuania. And this depends on "some" global settings.
Tbh I just stopped caring and now happily live in my little world where utf8 is the solution to everything, doesn't yield any problems ever, and anyone telling me differently gets completely ignored.