Have to say I am really bored of Legion and doing the same world quests again and again for 7 months now, there is a lack of content and to be honest now that I think about it I don't get the praise of Legion for the fast content release.
So far they have released 7.1 with Kara in which half the dungeon was a reskin so they didn't had to create any new art, only the later part is new and also much smaller. They also released Trials of Valor with art and bosses which already existed in the game they only made the mechanics. Lastly we got Nighthold in late January which while a nice raid was held back. Meanwhile there has been little to 0 content for outdoor only raids and a dungeon.
Mists on the other hand got 5.1 in late November, same time as 7.1, with new quests and a new faction, then we got 5.2, which is the equivelant of 7.2 with new raid and zone, in 5th of March. 5.2 had new art and new raid with little to new reskins while 7.2 is full of reskins (if I am not mistaken only the final 2 bosses are new designs) and new tier sets instead of reskins of tiers from the black temple.
Also the way I see it the raid content of MoP and Legion is comparable:
Mogushan Vaults = Emerald Nightmare
Heart of Fear = Nighthold
Terrace of the Endless Springs = Trials of Valor
In my opinion Mists had way more content and faster (since Mists was released late September instead of late August) so I really don't get the praise for Blizzard.