I'm actually goin to chime in and give my two cents on this quoted area here. The answer is: that both of these scenarios take a skilled group to pull off. Just as you have had your fair share with bad players being the ones to request smaller packs of enemies, I have had similar experiences with over geared raiders coming into dungeon, calling it brainless content and then they fail because they pull everything not noting the type of team they have to work with for the following reasons:
1. Lack of communication
2. Not even bothering looking at gear until the first wipe.
3. Asking the group if they want a SR, so instead they assume it (this also falls back to #1)
4. Brainless tanking, due to their ego and assumption that it is the healers full responsibility to keep the tank alive even if they stand in AoEs and not use their cooldowns, while spamming flash/OP. And yes I've seen this one ALOT.
5. Healers DPSing and not taking note of the tanks life and how much damage they actually take during large pulls.
6. DPS not knowing which skills to use in rotation to actually make for a successful SR.
All of the above (with the exceptions of #4 & #5) actually stem from communication.
This is not to say that all raiders are this terribad, but this is to give you insight from the other side of your question.
Bad groups fail from the start, only skilled groups complete the task, regardless of how many attempts it took to do so.