Definitely a good reason to use Qt, but you wouldn't get that with Delphi either. Qt is probably the best looking build-once, run with an acceptable UI package anywhere in that market.
EDIT: Just saw your second addition... not so sure I'd agree though, the performance on startup of .NET applications these days is quite excellent and I haven't been able to tell for years, but I've been on SSDs with lots of RAM on recent chips I suppose.
Delphi footprint is actually less than Qt in many cases (at least of older versions, don't know about the new ones). Don't forget that VCL wraps native widgets, so there's a lot less code in there.
I'm programming desktop applications in Racket, but unfortunately for many purposes it is, as of now, too slow. Especially application startup time is painful, and text% and other essential components of the GUI are way too sluggish for professional end-consumer applications. Maybe the Chez-based rewrite will help, but I'm not betting on it. Parts of the GUI library are just too complicated, and sometimes for no good reason (for example, style lists or the way it deals with snips internally).
I'm probably ending up with prototyping in Racket and writing the final application in Qt or Lazarus.
I believe there's a few things under .NET that try to wrap multiple UI libraries to varying levels of success too however none of them are as mature as Qt for a nice multiplatform UI in my opinion.
Plus I want it to have a tiny memory/CPU footprint and while .NET/WPF is better than the average Electron app I still notice a difference.