TL;DR: being an OCaml programmer now, and having worked with Ada (avionics/military sector) for a few years, my reply is: none of the two :-)

Long version: I should copy&paste your long version, I agree with your analysis. In my opinion the best for good-looking GUI is Python+PyQT, which is a really mature and stable environment. Avoid C++ + QT, it's stable of course, but using C++ in 2013 is a real PITA. Python is totally unsafe, but in tandem with PyQT takes you to a very fast and productive environment.

GTK: my personal opinion is that it's an awful toolkit, from each and every point of view. Bad software design, horrible widgets, etc... The OCaml binding is probably (from the programmer point of view) better than the original C API, but it's still a pain.

Just my 2 ¢ of course.

Paolo