You might have already read this advice, but it helps a lot to take it slow. Summon everyone you can, get on the horse, then wait for an opening, hit him once and retreat. Resummon characters as he kills them. Be careful, don't greedy.
I definitely wouldn't call that fight easy, it took me like five tries, but it seems like that's still a lot less than a lot of people. But it was by FAR the longest fight in the game, probably in any From game I've played. But if you lean on the summons and just chip in when he's preoccupied and run like hell when he's focused on you it's not that bad.
Been trying but the summons eventually just stop having their signs appear. I'll get him down to like 20% or less and around then the summon signs are no longer appearing ever. Eventually no one for him to fight and he just will find me no matter how far away I am, he will eventually get to me.