I really don't get this complaint at all. Blizzard have for some time been trying to push raiding as a base feature of the game, which means that it should come natural to you to raid. LFG is a insanely usefull tool atm and if you, as a player, can't find a group through this system with full "solo player" gear, then something is very wrong.
So if you really want this cosmetic weapen skin, then there is a very low bar-for-entry. But what if you don't want to raid? I understand that point of view very well, but then you should be used to not getting some cosmetic things all the time. We have always had gear, titles, mounts, pets and more stashed away in raiding, because some raiders needed another reward other then gear. So this is not something new, so the people who call an end to WoW because of this are being childish.
Some use the argument, that there are already few skins for the artifact weapen, so they are being pretty limited by having a skin locked behind raiding. This argument is both wierd and frail, since there is already a skin locked behind PvP and very few people have complained about that. So if PvPers are to get a unique skin for the weapen, then why can't raiders?
And yes, it is sad that Demon Hunters with their glaives, can't really transmog into other weapens, so they are locked into using their artifact weapen skins, but that is more a problem with the current way of glaives and not the unique factor of the skin.
All in all, i really think that some people need to pull themselfs together and ask themselfs how much value they are really ready to put into a cosmetic skin. If this cosmetic skin seems so impossible to get and so important to get, then maybe you should change the way you play or find another game to play. If normal raiding seems to hard to get into, but you still want all the benefits, then you are just acting like a spoiled child.