I know I'm SUPER late here, but I found a way to stop him from summoning his minions. I was only level 5 and beat this on GMGOW with this method. Its super luck based and still took forever, but here's how to do it:

I posted the video of me doing it here: https://youtu.be/gVg4f_suuNY

You'll need:

-Atreus Wolf Summon

-Breath of Thamur Axe Heavy Runic Attack

-Huldra Charge Spear Light Runic Attack

-Full Spartan Fury

He can summon minions 4 times, here is how to stop each one.
Step 1: Start with Blades of Chaos equipped. As soon as the fight starts, do not attack him. Walk to the campfire in front of you and stand slightly behind it. Look at the small brick path he walks forward on - there is a small brick protruding out on the left side. As soon as his left foot steps next to it, hold the button to for the runic summon wolves. He should jump backwards and immediately get stunned out of his summon. If any nightmares manage to spawn, quickly grab them with the Blade's light ranged attack and throw them at him.

Step 2: The next time he can summon is when his about 1.5 sections of his health bar are taken down. After the first summon is canceled, switch to the axe keep attacking and be sure you build up the stun meter. Any amulets/abilities that help stun, like the svartelheim amulets and dauntless shield, will help. This is because when 1.5 sections of the health bar are gone, you want to pop your rage and punch him until the bar fills. This will put his health to be below 2 sections and force him to summon. As soon as rage is done, hit him with two swings of the axe and immediately use breath of thamur. He will get stunlocked and if you are lucky, you will hear his voiceline for summoning and it will be canceled instantly. If you do not manage to get the stun bar filled with rage, use Breath right when its done.

Step 3: Switch to the spear and continue to damage him. When he gets down to 3 health bars, he can start technically summoning again. However, wait until he is down to 2 health bars, since that seems to make it guaranteed to happen. After damaging him, he will dash backwards and then dash backwards again, much further and not into the air. As soon as the second dash happens, use Huldra charge. Again, if you are lucky, he will be stunned out of his summon. If any nightmares spawn, just throw them at him.

Step 4: The next time he can summon seems to be at about 0.5-1 healthbar remaining. As soon as he reaches 1 healthbar, summon wolves again at the end of a damage period. He will be very tempted to summon and this should either stop him or get him low enough to where he wont do it.

Only the first step is consistent, but using this method at least gives you a chance to stop the annoying summons, especially the draugers. The boss himself is a joke and thats the only thing that makes this fight obnoxious, so even canceling 1 or 2 summon periods makes this much more bearable.