This is true, and currently is the biggest hurdle to solo content. Some just flat out have it easier than others or, in the case of Underpin ??, have it mechanically easier for no real valid reason.
I think they’re trying to fix that, but that’s a work in process.
Anyways, I can give my Hunter perspective! I’ve done 8 mask in both Org and SW. I’ll give my trouble spots and what I did. I did them as BM: I was face tanking too much damage as MM to get too far.
STORMWIND
Started in Old Town. Easily the hardest as the Inquisitors have the good ol’ Grasp Of The Abyss AKA “your run is over bucko see you next time”. There’s two scary pulls that you can’t really LoS: Right before the miniboss with 3 Inquisitors and the one right before Shaw with two, but there’s a ton of hidden Light Hunters that pop up and you risk pulling the pack right past the miniboss.
Freezing Trap helped a lot here, you can throw one on the Inquisitors at each pull, kill the other(s) and keep your pet up from the pummeling they’re about to receive. Be mindful of your kill count as Hogger popping up can ruin your day.
Outside of that? Take your time, keep health topped off for you and your pet and grind it down. Shaw is easy: Avoid eyes and step out of his AoE thing. You can usually position to use class abilities without facing him. You’d think, being the Rogue he’d know how to use Backstab but…I digress.
Trade is easy, bait Gift of the Titans or use an orb, kill first Miniboss. Convert is annoying because it will hit your pet and your pet won’t obey Kill Command anymore. Second miniboss is easy, and objective is easy. Zero problems.
Mage is an onslaught of Corruptions, stay near the entrance and grind them down. The casters are priority: Mind Flay does a lot of damage after Vengeance buffs and they’ll have plenty with all the Corruptions going around.
After the minutes of slogging away, make way to Big Corruption. Now while Leaden Foot will slow you down, keep in mind the AoEs are on a timer: Move, stop, move, stop. That way stacks are minimal and you maintain mostly full mobility to avoid the lethal frontal.
Ex-Warlock is a chump, which leaves Umbric. Now fighting him fairly? Yeah, you only can interrupt one thing. Missiles should be interrupted always: That’s a lot of Sanity drain. While Polymorph will also cause drain (You can’t avoid the puddles you leave) it’s much less than eating Missiles.
But there’s a fun trick. You can outrange both Missiles and Polymorph, and let your pets go to town. There’s a caveat in the way of you being out of range to use either Kill Command or Wrath, or heal your pet, but you take a lot less Sanity damage. I dipped in, cast Wrath and other abilities and tried to dip out. It seems when Polymorph is being cast you can’t outrange it, but he doesn’t seem to try casting Missiles anymore which is huge.
With pets, this fight is much easier. BM Hunter and Warlocks eating well.
Dwarven District is extremely trivial. AoE cleave all the mobs and kill Hogger a few times.
Alleria is likewise pretty easy: Don’t stare at the eye, stay away from bombs, interrupt Polymorph and avoid the AoE vomit.
ORGRIMMAR
I had a rougher time here than in Stormwind for the most part. Old Town was rough, but there’s a lot of nasty spots in Org too. Also the adds are a lot less range friendly with charges and other ways to close the distance, or not caring that you’re even at a distance.
Troll Town is the easiest. Zero issues outside of jumping off the bridge. Not much to say about this one. Remember to jump.
VoW is easy save for one pull: You have three Dominators with the pull close to the altar. Like before, Freezing Trap the one furthest to the left and kill the others quickly, stun if you must.
Big Orc isn’t a problem for ranged, but the Blood Corruption? Pretty spooky! Its AoE vomit is fast hitting and difficult to dodge without AoE. Leaden Foot doesn’t help, either. I had the best of luck staying close and moving through it while Disengage was on CD. You may want to Orb this one just in case as the AoE vomit drains a lot of Sanity.
Boss is pretty easy. Mind the frontal, don’t eat an orb, AoE corruptions down.
Drag is a drag. Miniboss is weird because the orb AoE gets caught up on the fences sometimes? Keeping a distance seems to be best because of this. Remember to jump. There’s some Dominators in the packs but there’s only one in one pull and two in another. Should be easy to burst down.
Boss is easy: Stay behind the tree and order pets to Kill Command a bunch. Use all CDs at the start so you can break the shields down (Wrath is off CD often enough with the set bonus so you should be spamming it anyway) and nothing to it!
VoH is rough only because of the pull before Rexxar. Most of the pulls you can avoid if you head towards the big building and go through the water, including the Elite. With Gamon showing up so much you can skip it without problem, which is great because it likes to drain a lot of Sanity for me.
For the pre-Rexxar pull, kill the Venomancer first, then AoE the rest down. Position yourself so the knockback from the big guy knocks you up the hill as opposed to down. Going down will knock you into the Elite and the other packs you skipped, with obvious consequences.
Rexxar is easy as long as you take your time. Keep your pet up, burst down the boars, save the stun for the Double Boar. Rexxar has no other abilities outside of autoattacking your pet. Just don’t step in the traps and don’t touch the Sha beasts.
Thrall is spookier than Alleira purely because getting hit by the frontal stun is a death sentence. You will pop a revive and if you don’t have a revive you’re starting all over. Pay close attention to his cast bar. In fact, just enhance it to be like 500x it’s size. That’s the only real thing you have to worry about because unlike the boss that uses it, it’s a lot more subtle.
There will be a lot of AoE junk on the ground but as long as you’re moving it’s not very dangerous, and his wombo AoE is easy to dodge. Just don’t get stunned, ever. Not once. That’s the frustrating bit.
And that’s my 8 mask journey! It’s hard, but I think most can do it on a spec? I guess Dormi can also help but only if you really have no other choice since it really makes the enemies a lot tankier.
You can get it! Best of luck!