Arguably they do have a difficulty curve. The first boss of any early ARR boss dungeon compared to ShB is quite different in difficulty or complexity. It might not be to a level you want it to be, but there certainly is a curve.
That is optional content not connected to the MSQ or general gameplay. The horrible players (5% maybe?) who are in question are either not playing these, being carried, or being vote-kicked. In the case of a carry, you have the option to vote kick or leave the party. At any rate, I can't believe you would encounter this at any regular rate unless your server is full of trolls.
That's not what is being discussed here (so I've been told). Most people playing are competent at the game, with like a C+ if we were grading. What you're talking about is a fraction of a fraction of the population that is largely trolls.
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Truth be told, I'm not sure this widespread problem of horrible players is even a real thing. I can count on my hand the number of times I've met a player in DF who was awful and refused to improve.. most have been very agreeable and open to suggestions.
Those that I did meet were absolutely trolling the DF and easily kicked.
(I play on JP server, full disclosure; where the clowns are usually the English speakers)
