While I agree that shared pointer are problematic (I almost never use them in C++), I don't think they're ever really the reason for performance issues in GUI apps. I've been doing GUI programming for more than a decade now and the overwhelming majority GUI performance issues come down to issues like poor use of concurrency (blocking GUI thread), unoptimised algorithms (e.g. for layouts), overdrawing, GPU/CPU sync issues or inefficient input handling.

I have never encountered a performance issue that was to due to reference counting (in fact I'm a big user of the CoW idiom when it comes to UI).