Take two deep breathes, then follow with me.
"Unique 5* materials guaranteed for each successful run"
This means every run guarantees you a piece of 5* gear as long as you're willing to alchemize the materials into armor. Now, let's do some math.
Let's assume you can buy a 2* piece of gear for 1.5k CR. The cost to get a 3* recipe is 4k CR, the cost to get a 4* recipe is 10k CR, and the cost to get a 5* recipe is 25k CR. Now, you also have to upgrade this item to 4* before you can do the 5* craft. This costs an additional 1k + 200 CE and 2.5k CR + 400 CE. All in all, this is going to cost you, if CE is worth 60 CR per, 1333 CE just to get an item ready to craft the 5* version.
This means that each shadow lair run is at minimum worth 1333 CE. This excludes whatever profit you gain from crowns.
This means even if you only get a shadow key in every five lockbock boxes, it can be worthwhile to run Shadow Lairs as long as you split the cost with a group. That is excluding whatever is contained within the lockboxes that could be sold. The value of accessorizes will no doubt go down, but any possible reimbursement helps make this a more worthwhile effort.
I would have preferred if it was easier to run Shadow Lairs, but this is what we have. You're able to do less runs, but each run is much more rewarding. It may actually save the bad players energy in the long run, as they'll have to do less trips reducing the number of potential deaths they'll face.
Interesting theory, would be good if the numbers work out similarly.