Without Threads of Fate, SL would be the single worst alt-leveling experience of all time, in my personal opinion. Even just heading to the Shadowlands zones in general gives me a headache these days. It's just so incredibly jarring and always an angering experience every time I go there.
Also, for the Mechagnomes, you need to complete a short questline in Boralus. You don't need to complete the dungeon. Even if you did, you can just do the M0 version of the dungeon and solo it.