It's the mechanics, how some classes completely hard counter others.
For instance with the valk, if you have low dps and no way of applying disease, it's
impossible to kill her.
I listed vamps because they are also one of the fumble classes, applying a debuff that lets your enemy miss 50% of his swings
in addition to capped evade rate + some parry and block is just stupid in my eyes.
The whole defensive mechanisms make this to a lottery game, have fun trying to hit with a 2h weapon.
The almighty answer is of course zerg them hard.
Also I don't know why armor resistances are still not neutral across all realms, take a spear hero for instance vs pole armsman.
spear deals 10% less dmg to him while he does bonus to you, which makes a massive difference.
All of that just adds together for me and when you have a tough solo fight which favours your opponent because of above listed factors,
3 scouts add and fill you with arrows(especially nice if you used all your active RA's).
Just makes me say fukc this... not even Darkfall makes me rage this hard when I get zerged tbh

And of course you need to pay for an extra bb account for all that "fun".