From a Tuning POV, I think you need to lower the HP of enemies by 15-25%. The Health Mod on single elites makes them health sponges. I think Damage Mods are okay for now, but your Systems team needs to consider lowering the time spent in combat.
The limiting factor tends to be defensives.
Idk why people keep saying you only get 4 keys. It’s incorrect.
You are only guaranteed to get 4 keys out of your first four boxes.
You are NOT limited to only 4 keys.
One takes 2 minutes.
One takes 10-15.
Gee. I wonder.
That’s like asking why M+ players run the shortest M+ when they’re only after vault.
Read how keys work and maybe I might give you a response again.
Ppl really be sleeping on this spell.
I think it got stealth nerfed on Threadomancers because they don’t even cast it anymore after that one hotfix lol.
So… are you telling me Maw of Souls wasn’t the most beloved Mythic+ in Legion? 
(Just adding to your point, ofc.)
People ran it because it was the shortest to run. Same principal here.
Loophole? What loophole? You do the mechanics, it’s not black magic voodoo. Blizzard even made it customised to every spec based on what interrupts/cc/dispels/anti-snare they have. Literally anyone can kill Zekvir Tier 1 if they are capable of doing mechanics.
That aside, Delves are tedious because they now take longer than they were marketed to take. The concept was a soloable bite-sized mini dungeon. Most dungeons are faster than any Delve. This is the real issue.
For just the reason you mentioned. Pound for pound they are easier, just as time consuming, and can be solo’d for the same effort as a Mythic, minus the people screaming about timing their key. I can AFK in a Delve, walk the pups, answer the door, open my stuff from Amazon and come back to no one screaming LOL Delves are one of the best changes to retail in a LONG time. Between Delves, Follower Dungeons, and Warbands, this may be my favorite expac of all time.
10-15? That’s how long it’s supposed to take. It takes almost twice that for most specs, on characters for which the rewards are still relevant.
So wait, the problem is people optimizing the fun out of the game even with delves and solo content? Man, what a world where one day players can complain about the meta and people sweating over small things in the next would have the same people upset that meta Speed Run Strat for the filling the vault got nerfed.
I would try to find some points to spare for that. The things you can MC deal a good amount of damage, specially the worm guys that have the AoE fear.
Oh… and here I thought I was fine having just a couple open each week. Obviously I’ve been playing the game wrong all this time.
Can’t say I’m surprised since it was much more convenient time-wise than T8 delves however it’s kind of a big bummer, specially for alts…
It was a nice way to quickly fill some vault slots for my alts since some weeks I don’t have a lot of time to invest in them and clearing T8 delves takes much longer. Also they are lower item level so it’s not easy to get invited to pug raids on them.
You can get more keys from Coffer Key Shards that you can get from using Radiant Echoes or occasionally from world quests.
just don’t worry about the 3rd delve great vault slot, problem solved. It’s there for people going above and beyond and is not something you are “forced” to do.
Hmm…
I don’t know I kind of do enjoy the new raid 
But I digress, I love the government cheese Blizz is giving us with Delvs and a great revenue stream for gearing outside of raids/m+ 
You can get more than 4 out of boxes. You’re just not guaranteed to get them like you are with the first 4.
The boxes can only give 4 a week. That’s a hard cap.
Nope.
I’m not sure what you’re basing that on.