Unfortunately, this will only get worse. World of Warcraft is losing subscribers, and Blizzard fully realizes they need to keep the current playerbase busy. That's why everything takes a fuckton of time to complete. That's why, currently, leveling alts is extremely unforgiving and time consuming.
Blizzard wants you to stick around to pay that subscription fee. They don't care about you, all they care about is money. I mean, the class advancement research alone takes more than a month, so if you want all that, you need to pay at least two months subscription fee.
Legion looks great, a lot of effort has been put into it, but at its core, it's a massive grind fest. A lot of content also stays releveant. The whole Warforged and Titanforged gear keeps heroics relevant for far longer than would normally be the case, as with Mythic and Mythic+. You used to be done doing all that stuff at a certain point, and that point will come for sure, but it just takes a lot longer than it used to take.