I'd say that's the rarer approach, though. Yes, some arbitrary-code-execution strats go that far, but by far most glitches used in speedrunning are found by either creative use of game mechanics, just screwing around in the game, or by accident (there are a few general techniques that can apply, e.g. wedging something into a corner and spamming buttons is likely to result in a clip or some kind of high-speed ejection, due to the general weaknesses of physics engines). Only a few, older, very popular games get taken apart to the degree you describe. Watch a few GDQ runs, and see how many times the runner goes "we have no idea why that works, but it does".