I carted and abandoned the quest a lot before I beat him at around 6'30. His attacks are slow but deadly, but they have very obvious openings. I think the key is avoiding all his abilities. I am a hh user and I slot in evade window 4. I believe it's really helpful.
flinch shot and tenderizing are quite dangerous without rocksteady and temporal. Other than that, make sure to read his attack patterns. Here's a few. Most of his attacks has accurate hitboxes.
- 2-3 rows. You can just walk or roll, but remember to roll out of the zone.
- random spots. Usually it's quite easy to hit his forelegs or head when he channels.
- 5 advancing rows. You need to roll towards him. The pattern is fixed.
Another obvious opening is the three explosions fire attack. Roll to the center after the center has exploded, and punish. Bring astera jerky. Good luck!