Oh by "more complex" operations I referred to multiple cursors and multi line regex searches. I've noticed some performance problems in my own editor but it's mostly because "lines" become fragmented, if you allocate all the lines with their own allocation, they might be far away from each other in memory. It's especially true when programming where lines are relatively short.
Regex searches and code highlight might introduce some hitches due to all of the seeking.
Kakoune has been my main editor for the past year (give or take) and uses an array of lines [0]. Ironically, multi-cursor and regex are some of the main features that made it attractive to me.
I just tested it out on the 100MB enwik8 file I have laying around and it does slow down significantly (took 4-5 seconds to load in the file and has a 1 second delay on changing a line). But that is not really the type of file you would be opening with your main editor.
Regex searches and code highlight might introduce some hitches due to all of the seeking.