Great analysis, spot on.
I ran it last night, took 15 mins to complete the level, 15 SOT - got a 1* red evo rune and a 2* red evo rune. Something must be off, that can't possibly be how it's supposed to work.
On another note, Shadow Of The Valley (the 6th level) in Underworld is dropping multiple 3* rainbow evo runes almost every single round. I'm up to 228. So if you're looking for a boost in evolving these talismans, head on over.