As much as I'd like everyone to be equal, I can honestly say - as someone currently raiding on a ranged, but who normally plays melee - that it should be like that. Melee struggle enough for raid spots as it is, without damage on top or specific mechanics (rogue feint tanking shit like Blackhand, etc) then why would you bother taking melee? Ranged have it so much fucking easier in the average, non top-50 mythic raid/dungeon where mistakes are made often, it's unreal.
As melee, you're at the mercy of the rest of the raid not making mistakes (mostly tanks and other melee, but ranged/healers too) and doing things like positioning the target(s) correctly or not dropping shit where you need to stand to hit the boss, great you can dps on the move, but that's useless when there is shit between you and the target, or hell, half the time it can be under it because the tank doesn't feel like moving - or does, but slow enough for you to be forced to take damage or stop dps. Ranged might have to stand still, but I'd much rather be at fault myself for poor pre-planning than at the mercy of someone else.
When I first did Helya on my [MM, still needs to stand still unlike BM] Hunter I was amazed at the fact they could be nearly at the water at the back of the room and still deal full damage - when oozes came I could DPS them immediately with half a step of movement that was on-GCD and zero DPS lost [pre 7.1.5, don't need to move at all now, RIP Sidewinders], or without standing in what they dropped the breath before that - or that I could continue to deal most of my damage whilst running away with an Orb. Any of that is a DPS loss or damage taken as melee.
I'd much rather play my Rogue - and trust me I know I have it easy for mechanics on that with Feint/Cloak relative to the rest of melee - as it's more fun and engaging mechanically. But why would anyone bother when you can have it so much easier? Have fun playing favourite spec/class, have to deal with other people's mistakes - or have less fun, but have to so much easier and not have to put up with other people's mistakes costing you damage constantly.
Probably got a bit carried away, but tl;dr - I'd much rather everyone be equal, but whilst ranged have higher uptimes, I'm not surprised melee are higher on damage. That should equal out though in real world fights, so, it still needs changing I agree.
Yeah, if a class is doing noticeably more damage - be it overall, or to specific targets - that make a fight easier, it will get noticed and a "meta" will form around it. pre 7.1.5 Hunters on Helya for example, for the oozes. They weren't amazing overall, but they make the fight so much easier when people weren't worrying about Oozes.
That's literally the reason I switched to my Hunter again so my guild would have an easier time on HC Helya. Literally jumped in, 15-20 ilvl lower than my Rogue, and went from doing naff all damage on Oozes and requiring all the raid to switch, to topping damage by far and letting two other people stick to the boss instead. Then we got another Hunter. Lulz were had. Half the time they ended up dead before Barrage if we were lucky on Marked Shot proccs.
I guess that also fits into my above comment: Why bring a melee when you can bring a ranged that makes the fight easier for everyone else. ¯\_(ツ)_/¯