Qt runs like shit compared to Electron, and its license prices are way too expensive. Moreover it's C++ so a deprecated, unsafe, un-cool and uninteresting dying language no one wants to write anymore.
Or better yet, make a web engine from scratch, that is, write the rendering engine, compositing engine and so on using Electron primitives.
Because both of these work very well when using Qt as a base, see LXQt and KHTML.
JS can get close to C++ in speed but the same program in JS will always need more memory.