I feel it very important for you to realize just how important individual skill actually is. How skilled you are is an individual relates directly to your ability to contribute in a group setting. If you perform poorly, you could easily be the reason a group gets wiped by an enrage rather than managing the clear, even should the other members of that group be performing their roles adequately. You assert that any challenge in this game can be overcome solely through teamwork, and that as a result of this the perceived difficulty of content is in no way related to player skill. However, I submit to you that your skill as an individual is in fact integral to and reflective of your ability to work as a team. Lack of coordination in a team, even in random PF learning groups, can often be traced to players that are making no meaningful progress in their personal fight understanding or teamwork, as the two are indeed demonstrably linked.
The vast majority of players are unable to work effectively as a team. Even when taught how to do fights - even when provided with callouts and markers, most of them simply cannot or will not do it. There are also those that have the potential to improve to that degree but become demoralized and ultimately give up instead of continuing to push themselves. Additionally, it is important to consider that what is difficult for one person might not be difficult for another, which is why we use the majority as the basis for determining the actual difficulty of content relative to player-base. A minority being able to overcome a challenge does not mean everyone can, or that they would be willing to try to begin with.
Now, to your last point; the failings of others are not my responsibility. I'll gladly go out of my way to teach people that are willing to learn, but the ones that can't or won't, which does sadly appear to be the majority, are not problem. If being unwilling to tolerate those that won't better themselves means I'm "not a good team-player," that's fine. My opinion hasn't stopped me from clearing content, and it certainly won't magically start hindering me now.
That one I can't figure out. Do people just use "farm party" to bait players in? 'Cause I'm really starting to think that might be the case.