Flutter / Dart? It's compiled ahead of time and doesn't use an embedded browser so I'd expect it to be a lot lighter, though I haven't measured.

But the general lack of really cross-platform (desktop + mobile + maybe web) ecosystems is just as much as sign that devs consider multi-gigabyte Electron apps "good enough" as the apps themselves.

Reliable as in "exposes the same bug across all platforms"?

If you are willing to ignore accessibility, your statement is right.