Why are low standards for dps acceptable?

[Granyala]

But what we have been shown in the image is "hello?" "is anyone there?" "is this a bot?" which isn't exactly a nice way to engage someone in a lesson.

Correct, and I'd be willing to wager that this aggressive opener was the reason why his words fell on deaf ears and ultimately why he was kicked.
Criticism is okay, but keep it polite and constructive. Stick to the mathematical facts and don't imply any personal stuff.

That being said, you WILL encounter people that think they are gods gift to the gaming community and that take even implied criticism personal.
In that case it is best to ignore such a person, as your efforts will most likely be in vain.