Don’t design around computational addons at all. Like they don’t even exist. Test mechanics without them and give computational addons no other thoughts. The advantage they would bring wouldn’t be able to exceed human tolerance or capacity then. This way mechanics stay sane and reasonable and there’s no need to nerf an addon. You could disable the computational parts of the API on PTR too maybe. Or just the few specific troublesome addons so that people test the actual raids. And not their software development skills.
Skill between mythic world first guilds who choose to use the addons would then come down to gear, talents, comps, and rotational strategy. And the raids would still be doable with or without the addons. The majority of raiders and average players would find raid mechanics much more suitable.
That said addons shouldn’t be able to play a character or click buttons. Afaik this is already the case.