Like you, I am excited to see this approach. There may be a lot of negative opionions about Electron, but you can't deny the inroads it has made.
With that said: I got the sense the author is mainly interested in targeting high-complexity desktop apps, which tend to have less need to be available in both forms
1) Packaging/general polish. With the server solution the user doesn't get a desktop icon, or a single .app/.exe, etc. Their window manager doesn't work with the app the normal way. Etc.
2) Certain other native integrations. An electron app can populate the Mac menu bar, it can use native right-click menus, it can do rich notifications that aren't constrained to the browser's notifications API, it can show a red dot in the system dock, etc.
3) Stability of pinning to a specific Chromium version.
This can work for some things- mostly developer tools where users may not care as much about polish and may care more about reducing install size. But it's not really a replacement.