My response to this will be somewhat long and meandering, and I apologize if it is somewhat abrasive.

I think my problem is I reject at its core that any single one person is "Dragging" a party down by failing a mechanic. And in many ways I think that kind of thinking is kind of... harmful to an MMO as a whole, because there is no such thing as an individualistic failure or success in an MMO. In spite of the fact that very many people would much like there to be someone to blame if a failure happens (because its easy and comforting, and it allows them to think success is individualized) it just simply isnt true, every failure and success in an MMO is a result of everyones action in a team.

In the example you gave of coming to a duty finded instance later when everyone knows the mechanics, heres some of the things that any one in the party could have done to allieviate a situation like that:

1. A healer could rescue you out of a mechanic.
2. Someone could mark someone who does know the mechanic and say "follow them".
3. They could explain any tricky mechanics. (you could even make macros for especially common ones so you dont have to type it out each time)
4. They could vote kick whoever doesnt know or failed the mechanic. (on the mean side, but certainly an action they could take)
5. They could have not used Duty Finder to do the content, instead opting to use Party Finder or a pre-made group of people who know the fight.
6. They could have also just not done the content, if the prospect of potential wipes or failures was too much to bear in spite of the rewards.

These are all options available to them, and while yes some responsibiltiy lies in the person who failed the mechanic, ultimately all of these people have responsibility for their own actions and choices to do content which is designed for people to fail at least somewhat of the time. And hopefully people who go into that content do so always knowing failure is possible and adjust their expectations for that.

While I have a lot of empathy who can't help but feel that kind of personal responsibility on failure (I struggle with it a lot too, especially in EXs when I mess up a mechanic), I think the benefits of having these kind of mechanics which in some ways "artificially" increase the failure rate of content is a good thing, because it serves as a constant reminder to everyone who does content: failure happens, and it is natural.

Hopefully that helps foster in people a more team oriented attitude.