The vimscript implementation doesn't have many of the innovations of modern scripting languages. No JIT, pretenuring, inline caching, etc.

All your "one OOM away from VSCode" scripts run in a script language that is in the slowest category among all programming languages: interpreted languages.

There are probably millions of dollars invested in making scripting languages like JavaScript faster, but that's not the same case for vimscript. Same applies to other languages behind IDEs such as Java. So that intuition is not true.

With hardware accelerated widget toolkits, the TUI advantage is not necessarily true either.