using js for an mmo, a performance critical application, sounds like a big difficulty.
Software bloat and general lack of performance continue to be among the chief complaints end users have.
Not saying you're wrong, of course. The guy who passes the finish line badly wins the race, not the guy who fails the race goodly or the guy who doesn't even start running perfectly.
And if one ignores the mmo part and thinks of other show HNs, one can assume it's 300 lines of js in the main app and 2.4 gigabytes of js dependencies including 10 separate tracking frameworks...
Most of these projects exist in c++ already, they literally exist as the majority of MMOs, not sure what blather to justify your own bad architecture decisions you're on about.
Node.js is fine on the server and JS is my preferred language. That said I switched from VSCode to vim a few years back because my laptop couldn't handle all the Electron apps I had running. Now the only browser instance I run is the actual browser and I'll never go back to Electron apps.