To complete hellfire assault you need to be fast, get the crates they give a speed boost and be smart about you use it and you will be able to complete it.
Run hfc in a group until you get a skip portal (4 weeks of farming)
If you entered a mythic raid with people you are saved to that lockout. You cant just leave and reenter mythic difficulty.
It’s actually soloable now, and afaik it’s being made even easier in 8.2.
A cool trick is to make use of the 15 seconds window of speed boost you get after picking up a crate and actually clearing everything there will come a window where mobs stop spawning for some period of time.
It’s annoying yeah, but you either do the long method or wait for 8.2 where someone reported that 2-3 cannon strikes kill the boss.
I’ve not tried recently but before 8.1.5 it was a pain in the posterior to solo. I have often helped a friend just on first boss and then left them to carry on to clear the rest alone.
I would say they are catering even harder to a more casual playerbase than they have in literally years if not forever.
And I also think it’s a lot more than 15 guilds doing mythic content… Granted it’s far from the majority of players doing such content but that doesn’t mean it doesn’t have a place in WoW.
its been made easier , but 8.2 will make it super easy like cannns take basilcy no dmg.
And gear scaling wouldve been nice while current, betwene world first kill and speedkill over year later it only sped up like 20-30seconds or something