We already mentioned that there are two versions of the Qt Quick Controls module—Quick Controls 1, which were designed for the traditional desktop environments, have a very broad scope and provide a flexible styling system.
The second version, Quick Controls 2, are specifically designed for embedded systems where the hardware has limited resources, have an optimized implementation (for example, the internal event handling was rewritten in C++), and no longer support pre-built native styles. This all results in better performance compared to Quick Controls 1.
We already mentioned that with each new Qt release, the QML performance gets better. One of the biggest improvements in this field that came with Qt 5.12 was the introduction of the TableView item in Quick Controls 2, sporting a much better performance compared to the old TableView in Qt Quick Controls 1! The reason for the improvement is that the old TableView was implemented on top of ListView, which is optimized for displaying only a single column. Because of that, the old TableView couldn't achieve optimal performance. The new TableView was reimplemented in C++ on top of the Flickable item and seems to scale up to models with thousands of elements without performance problems.