That may be true for Python, but the Common Lisp bindings for Qt4 were equally as "powerful" as the C++ bindings. It had higher level abstractions that generally made it easier to read and write, as well.
> Bindings are not C++'s problem
Actually, bindings are a problem with C++. Some features (like templates) and implementation details (like name mangling) make it very difficult to create bindings to C++.
QML, Swift, Android, UWP, WPF, Forms, Blueprints, Unity, React Native.
QML is way faster to develop in than C++. And it hides a lot of signal/slot boilerplate that doesn't matter. And I can still write C++ classes that interface with QML when I want.
I agree, not necessarily with c++ but it's much better to build UI's with code than declarative xml crap.
It will be a shame if Qt sticks to a pure c++ interface though, I'd hope the build something more usable from more languages so it's an option for C, Zig, Rust, etc.
Gives the basics of the difference
Declarative UI languages do have some advantages compared to regular programming languages, but that's unrelated to the claim you made.
Bindings are not C++'s problem, they're the problem of the other languages which try to use UI frameworks written in C++, like Rust, which still doesn't have any decent UI library.