I have one Epic and Zero Ur in over 250 boxes (last event included)
Do not underestimate those Upgrades!
Each upgrade gives you 51200 TP, which is the same as 4 Superior Upgrades.
Each Superior Upgrade would consume 1075 Dil, x4 = 4300 Dil.
Worse case scenario you pay 40,000 dil to get 10 UC = 10 Upgrades.
Those are still worth 40 Superior upgrades = 43,000.
So even then you make a good deal.
Now let's take your drop example and count 6 UC, 3 Rare and 1 VR = 16 Phoenix Upgrades.
Those are worh 64 Superior Upgrades / 68,800 Dil.
You always come up ahead if you get the 10 pack Phoenix boxes, no matter how bad you luck is.