Cast sequence macros can no longer enable a 1 button macro for ones class rotation because they break as soon as the first GCD is reached. Which means that most cast sequence macros will only have 2 or 3 abilities/items attached to them.
So you can have this as a macro (as bad as it would be to have).
/castsequence 6, 10, Arcane Explosion
6 is your belt (Nitro Boosts), 10 is your Gloves (Synapes Springs) both of which have no GCD, Arcane Explosion has a GCD so now the sequence is closed and will revert back to the first thing in the sequence, 6 (Nitro Boosts).
This no longer happens and was only a thing in Classic, people were expecting it to be a thing in TBC with their one button Hunter macro but Blizzard broke the macro.
What conditions are you refering to because you can do this but it’s nothing what you’re likely thinking, please provide an example of what you’re refering to.
So you’re just against addons in general then, addons which have been part of the game for over a decade… Bosses just don’t telegraph their abilities well a majority of the time so addons like those are kinda needed.