I think the problem with ncurses (and to an extent readline), is that it was one of the very first apps/libraries and came out before various standards became the norm.
Leaving aside, the issue of /usr or /usr/local, there is:
* headers in include or include/ncurses or include/ncursesw
* headers named curses.h or ncurses.h
* no *la files
* pkg-config files in share/pkgconfig rather than lib/pkgconfig or missing entirely
* all functions in one library or split between ncurses(w), tinfo(w) and another lib I've forgotten the name of
As you say, some packages find tinycore's ncursesw as-is without problems, but many do not.
For me, the most obvious solution is to use the pkg-config files, but strangely, many of the apps that use pkg-config to find everything else, do not use it for ncurses(w) - cmake being the most obvious offender.