Troll thread I'm sure, but there's the thing.

You can't just lock people out of DF because it's required to progress through the game.

And if someone gets locked out, they can't improve.

How do you tell if someone's having an off day or if their bad performance is normal? For example on my ninja one night I was tired and just trying to cap tomes before reset and was doing EX roulette. I"m normally pretty good at mist draogn but because I was tired, I spaced out and stood in an aoe and died. How do you determine that from someone's normal play? Or what if someone legit has a lag spike etc?

If you run into someone who is playing terribly, you have a recourse for that. Vote kick them. That is part of the reason the system exists.

There also isn't a way to really enforce this. What are you going to do, have the game log everyone's dps and kick them? What about tanks and healers? How does the game tell the difference between a tank or healer being at fault when a tank dies? It's just not feasible to automate this kind of system and it would be phenomenally stupid to allow players that kind of power.

If you run into so many people that are below your standards that this isn't feasible, then vote kick them. If a dps refuses to use aoes for example, vote kick them. If you run into so many people below your standards that this isn't feasible, well then you're better off just forming a premade.

Duty Finder is used for easy casual content, In party finder, there's no excuse, a bad can be identified and kicked from the party by the leader.

You're always rolling the dice with random players in duty finder.