I have one suggestion to fix this an that is to half the majority of the requirements to complete each part of the quest (for alts only ofc after u have it on a main).
What are your views??
I think the grinds should be entirely removed, but the story and challenge elements kept, IF you have the cloak on any of your characters already.
Obviously, if you try the challenges too early, you will fail, so you can't get the cloak for your alt.
Point is: these quests - especially the 3k valor - were meant to put in some gating. Randomness screwage aside, once you have 2x10 sigils, one can assume that you're strong enough to face the first challenge. And so on. If the challenges stay, I can simply not cheat my way forward. Either I'll play LFR anyway, or I'll obtain appropriate gear another way.