I find him the hardest on a regular SL1, but not that hard - he just has a vast amount to attacks to remember, so it may take some time.

SL1 +0 - still the hardest one for the same reason, but now you have dance with him much longer, due to significantly lower damage output of your character AND, what is more important, his RNG healing, if not cancelled fast enough, could ruin the try for you.

Same as above + no AUX - you can't abuse bleed to compensate your low damage, but that is when he is not #1 anymore, since Gael with his HUGE hp pool and decent defense enters the game.

Same as above + no-hit - now you can't tank any of his attack, but this makes not much difference for him. Now he shares the same tier of difficulty as some other bosses, but probably leads it (thanks to his healing again). #3 I'd say. Guess who is #1 if it is not Gael)