They should've just made Torghast it's own endgame content without being a necessity for raiding/m+/arena (except as a bonus), then people wouldn't have hated it. Those that really like it and wanted to see it expanded could keep playing and those that didn't enjoy wouldn't be forced to do it unless they were tryharding. It could've provided it's own unique gear and rewards which can be decent for other content, but not the best, but they'd be the best gear for the open world and Torghast itself, just like how it kinda works with the gear you get from group content.
Especially in the rewards department is where Blizzard always fails at single player content. These things never have their own class of gear and progression, but it's mostly just one time rewards you get and stuff that is needed for other content, but has no direct or extra benefit to the content you just had to do (like the legendary system).