I'm going from memory here, time marches on never-ending, so please forgive me. I conflated two things: my performance test results are from the first 5,000 lines of Moby Dick. Why 5,000? One user has a 5,000 line taskpaper note file. But the whole 22,000 line book loaded and scrolled and edited just fine (after I fixed some bad assumptions that resulted in bad code). On iOS, I think if you're working on a file of 5,000 lines then something might be wrong, and if you're working on a file of 22,000 lines well I don't know what to say.
I definitely need to edit files that are hundreds of thousands of lines once in a while. Nothing wrong with it, I think you're just assuming it's source code or such when it isn't. It's often data manipulation (CSV, JSON, etc.) and it feels like torture when the editor can't handle it. I've even opened multi-gigabyte text files in my editor and needed to edit them sometimes.