You are being fairly logical about this (which thanks, it frustrates how most people aren't). But you seem to be making several assumptions here that are fundamentally not true for everyone.
First: I agree that players should not be lying about experience and joining parties that are looking for it. It is almost always frustrating both for them when they constantly get kicked, and for the party who is just trying to down content they already know. That isn't at issue here.
But second: this isn't a job to me. It isn't school. It is a game. For me, the fun is in solving problems. Not solving them first. But solving them at all. Why play a game where I have all the answers? Why pull out a puzzle and then follow someone else's exacting instructions to put it together? The fun is in the solving, not merely in the completing.
Efficiency says I should always try and find someone else who did something first, so I don't have to. However this is a game, which I do not even play professionally. For the challenge of solving things. Efficiency is only as relevant as the person's approach to the game.
I have no interest in being world first. What does that have to do with challenging myself? Therefore your argument that I am merely "emulating" those who came first is false, and irrelevant. I don't care if someone else has done it first. I get no thrill out of trying to tell other people they aren't as good as me and aren't allowed to challenge themselves because I did it first.
I don't care if I am the best player. I am not. I am however above average. This is something it took me a long time to realize, as I assumed I was well below average. But since I really don't care about being best, merely about enjoying myself and solving problems and formulating strategies on my own merits, it doesn't matter to me how much you try and convince me it isn't as efficient, or I will never be as good. That isn't the point for me (though clearly it is for many people).
My opinion on this, as it always has been, is that those who have a problem with other people playing "lazy" and "inefficiently" should stay away from them. They do in fact have the right to form experienced parties only. And kick people who lie their way in. But, this does not mean they also have the right to tell those other players how to play in general. Only how to play if they are going to play with them.
That seems to be a fundamental difference here: I don't force myself on experienced people. I in fact will warn people ahead of time I am going in blind, and that I have no interest in being hand fed answers. If this is a problem, I will leave, or they will. No hard feelings.
So for those who are arguing that people should conform to the rules of the PF, and not try to group with them if they won't play the same: I absolutely agree. But that doesn't mean I think it is required in general, or should be put out as the only way to play.
As for DF, it has always been for people who don't have access to an easy group so they can progress (and yes practice). So you will always get people of different mentalities. You can't avoid that. So know going in you can't control the situation and be okay with that, or don't join.
Until they add options to DF to try and segregate players (which I honestly never see happening), this will always be the case. Personally I often join DF titan to help groups learn. I find it fun when I get a group that is actually willing to learn. The rest who constantly give up, never learn. With or without videos and tutorials. The things that holds back DF titan is the lack of willingness to learn. Not the lack of research.