Yeah I mean I had complex thoughts like that but to be honest at the end of the day BLIZZARD DOES IT ON PURPOSE. The proof is the obvious common sense that if they wanted to nerf ALL THREE SPECS of mage (example) they would do it.
Since I see this trend for many years I believe it's basically "this dude only plays dps and has no other specs so he MUST not be below some other dude that has tank and healing specs too (or at least not noticeably)" and it's kinda fair to some limited extend.