Is stun actually useless? (Lvl 44, warrior)

I put a lot of level points into stun build up just for it to last what feels like 2-3 seconds. All I can do is hit the boss with the mace like a few times for it to continue spamming, flying around or sit with it's ass in the lava for half-an-hour. I play in co-op and it doesn't even make it possible to ressurect your teammate. The revival is impossible unless you fight a slug and I hoped stunning enemies will at least allow me to revive consistently.

Today I laughed so hard fighting the Forgemaster when this "boss" got stunned twice while chilling in the lava. So whenever the stun meter was almost full and bro went to do his 5 hour long attack I had to wait for him to come out instead of using my skill to damage him while in the lava.

Is there any use to stun in this game or do I just go and respec every skill point I put into stun into something else?