Yeah but that's not a realistic usecase for most users/developers. I haven't measured if Ox is faster or slower, but for me startup time and ability to quickly open files under 10MB are more important.
It also looks like vim and emacs don't decide what a realistic use case is, or if you're "most" users/developers. They just open text files for editing.
Even for large files, I've never noticed anything beyond microsecond-type delays with those. Definitely does not feel laggy to me, usually.
My beloved vim doesn't fair so we'll. VScode does very well on this.
I often find it's much faster to pipe out to a command line program to do formatting on huge files.
e.g.
:%! jq
:%! xmllint --format -i.e. I would have done:
:! jq %
:! cat % | ...