I posed a simple question to get a simple answer in order to further the discussion past the question of "skill".
I acknowledge what you're saying, but if I'm being honest it's just a lot of fluff.
However, you answered the question amidst the fluff, so moving on:
Since Speedrunning typically requires more skill from the players than single-pulling, it can be assumed that people who opt to single-pull tend to be less skilled than people who opt to speedrun.
/topic closed
Back on the original topic: Why do you, in-particular, dislike speedrunning? =3
Generally speaking, you're right. But I would say it doesn't flatline after 5; but the increase isn't exponential anymore. It just requires the tank to be better at cooldown management and the healer to know when spikes are coming and be aware of what the tank has available.
Large pulls definitely take more skill as well as gear to pull off, but once you have the gear, more skill will let you get away with more.
I think what makes this topic so sore to some people is that they're used to other MMOs, where dungeons are challenging in their own - or can't be steamrolled because trash have mechanics or abilities that make it impossible.
This is not so in XIV.
I think it's a flaw in XIV's dungeon design. A flaw I would like to be alleviated. But as it is now, speedrunning is prevelent in the community. While not at all an exhaustive study:
shows general community sentiments; and will get slightly more accurate as more people vote on it.