I'm on a moderately complex UI right now, that has a JS payload around 364kb gzipped, react-dom, chart.js and material-ui/core bits accounting for most of the heavy bits. I've also been heavy handed with pulling out libraries that could be done easy enough with just React and JS. Svg is suprisingly easy in React, and a couple events while tricky aren't as bad as some other tooling I've used in the past.
Overall it loads in right around 1s, as I mentioned the splitting for async load on demand doesn't work at the moment, which I had the initial load for a page not using chart.js down to around 115kb gzipped. Part of that also includes the embedded SVG icons as well as the JSS for styling.
It's not paying attention when lodash + underscore, + rambda + momentjs, etc. all get loaded via dependencies... most of that can expressly be avoided with specific smaller frameworks and tooling.
https://i.imgur.com/gf5cpNd.png