If you managed to beat them on your first try, I'm going to simply state, you got lucky.
I guess you could say that, but the Berserker has reckless attack which allows advantage on attack rolls so you will have a rather hard time missing, also, while you are in a frenzy I think you have 50% resistance to slashing/piercing/bludgoning damage. Add to that that it was a dwarven Berserker so we had 17 starting CON and STR, both of which were 18 at lvl 5. Tons of HP, tons of damage, wearing the Helmet of Grit allows the guy to have 2 bonus actions that you can use for attacks in a frenzy.
In my experience with this game so far, Wyll is the best single target blaster companion, and at lvl 5, he can have 18 Cha and his Eldritch blast shoots 2 projectiles. Add the Hex spell to that and he is basically going to murder almost everything very fast. And Eldritch blast can crit as well, meaning that he can deal some hilariouly high damage.
Only these 2 guys are dangerous enough, so maybe I just picked the right guys for the job, but I think many things depend on your class selection.
