The absolute numbers aren't that different. You need 100s of MB just to display an empty Chrome window. Then the 66% is the difference excluding that baseline, e.g. it might be 300MB to load Chrome, then you measure 301MB vs 301.66MB. I guess that might be a bit misleading.

I think the electron memory usage comes down to the massive HTML spec and bloated old browser codebases. It's not JS. Node+V8 doesn't have nearly the memory usage of Chrome+V8.