I've worked with Qt about 15 years writing several applications both for work and for fun and overall I think it's a really powerful platform. Not without it's idiosyncrasies and quirks of course.

That being said I find that QML is complete trash. It's fine for simple UIs with minimal logic and prototypes but for anything beyond that you'll always need to implement the logic in C++ and this is where the pain enters the picture. A lot of effort will be spent maintaining the glue code that lets the two worlds comminicate. The tooling is poor and QMLs poor typing makes it hard to ever change anything from types to available methods..

Generally speaking QML has terrible shortcomings in its lack of good typing, debugging abilities, error reporting or general maintainability of the code. It's your typical "write once" platform where the cost comes later if/when you need to maintain and evolve the software later on.