Objective-C was doing sufficiently-fast UI updates for it to run well on iPhones 10 years ago, while relying on objc_msgsend, which is _much_ slower than a virtual function call or even a Qt signal.

You wouldn't want to use ObjC's message sending OR Qt's signalling mechanism in a tight inner loop – hell, you probably don't want to deal with the indirection of the vtable incurred by a virtual function in a tight inner loop. But all of these are more than fast enough for interactive UI work.