Those factors are player dependent, and are often products of poor play. Sure other factors can lead to such outcomes, just like in the case of a dps doing lower damage.
Though personally those factors are irrelevant to me, I really do not care why someone is under performing I just care about the numbers.
Your stance would require me to care about such things. This is my my view for underperforming is fairly straight forward and black and white and I get for many that is weird and unnecessary.
I just do not get why people are willing to defend certain aspects that are a product of poor play yet blast others. Largely based off the role in question. Cannot tell you how many times I have seen people yell at a tank for not having tank stance on yet say nothing when the dps does not AoE. From a game play perspective both are moot in large portions of this games content. I have cleared content with 4 dps. Most content does not require fully functional roles yet for the most part they use the same line of thinking one has a higher risk of wipe which makes it an unnecessary risk so to speak.
When you bring up the risk of a wipe is still the same in the other cases of under performing once again told the same thing it is not very likely so it is moot.
In the end people are right the group can largely make up for many shortcomings for lower dps and I also argue the same could be said for healers and tanks, but I will concede that it is fair easier to make up poor damage then poor heals or tanks.
Though personally the degree of wipe potential or how much easier one is over the other is not grounds to give one role preferencenal standards so to speak and not the others.
So personally this is why I hold each to the same standard. Want to underperform by my standards cool do you, but if it happens to be in my group I will vote to remove them from the group. I see no difference between a non aoeing dps and a healer that just stands around between heals. To me they are in the same boat as the tank that refuses to put on tank stance or the afk let eos heal sch.