The berserker is meant to be the subclass that most heavily incentivizes investing in armor. For some people, who already like defense, this works really well, but lots of folks (especially more experienced players) are used to evading attacks and investing in high damage output, and so berserker doesn't fit their playstyle very well. It's also a bit unfortunate that a lot of his special power has to be so tricky to access compared to other subclasses, but it's sort of necessary given how powerful all that extra damage and defense can be. Older iterations of the berserker did things like granting the ability to cheat death for free, and were absolutely busted in terms of winrate as a result.

Berserker responds quite well to armor investment. You can consider his rage to be compensation for the damage you lose by investing heavily into armor.

With all this armor, if you can get a flail or glaive, you can safely augment them for damage to give them absolutely absurd damage scaling (they gain 1 min and 8 max damage per upgrade and have impressive base damage, after damage augment it goes to 1.5/12 damage per upgrade). Glaive is heavier and slower, but it does have +1 range to allow you to fight scorpios.

Just be wary of magic users. Take Improvised Projectiles as a way to shut down surprise warlocks, and look for movement boosters (especially chains) to help close the gap on these foes.

I find it quite hard to stay at low health and get out of the mindset of chugging a health potion. When I play it I don't normally invest in the low health talent. I do find both warrior classes less fun to play than the other ones but sometimes if I fancy an easy game I go warrior. And then will choose beserker or gladiator depending on whether I have better weapons or armour.

I have no idea how to play it, therefore it's terrible.

For real, I have no idea how to make the class do anything useful. Might as well just throw crown in a chasm.