I see both sides of the argument. It's supposed to be a hard fight, but also the time waste of repeating easier parts to get back to a hard part is a horrible punishment that videogames do. So I guess I can support the idea of putting checkpoints in long fights. Like you could make the mechanics even more difficult to compensate for there being a checkpoint in the middle and it would still be less stressful because eliminates mindlessly repeating phases you already cleared. Unless it's like Ultimate difficulty which is supposed to be masochistic, then you can have insane mechanics on top of no checkpoint.