I can see if you need to edit multi-gig log files and things will not fit in memory, but for small files, array is totally fine.

There were other tricks that were done back then to keep the number of single char inserts down to a minimum while typing. Like reading chars into a small buffer during fast typing and then inserting all the keystrokes at once as soon as you had the time.

But when pressing enter, pasting a bigger snippet, or deleting lines the slowdown is less noticeable. When you type a word, the deltas are tiny and it is easy to process for your brain. While the changes in multiple lines happen less often, so waiting a couple of frames doesn’t bother you much.

This is at millions of lines. With small files it is indeed too fast.

all of my C homebrew editors have been gap buffer based, and I told myself I'd reimplement if I ever wanted to edit something large enough for that to be a problem — but it never was.