React + ReactDOM adds ~50kb to a production bundle, not even close to a couple of mbs. React with any popular routing library also makes it trivial to lazy load js per route, so even with a huge application your initial js payload stays small. I ship React apps with a total prod bundle size of ~5mb, but on initial load only require ~100kb.

The idea that React is inherently slow is totally ignorant. I'm sympathetic to the argument that many apps built with React are slow (though I've not seen data to back this up), or that you as a developer don't enjoy writing React, but it's a perfectly fine choice for writing performant web UI if you're even remotely competent at frontend development.