Genie and the Goddess Of wishes
For statistic nerds:
Genies seem to average ~50 diamonds/week* each. I win enough Genies to keep 3 in place at all times, playing the full Spire each week. (*Genie average tracked over ~12 weeks with 3 Genies in place. Actual average was a bit higher; maybe 54 per?)
Between individual prizes for completing the Spire & doing Genie pick-ups ~10x/week, I was averaging 715 weekly at the end of December (10-week average). My FS historically hits silver around 40% of the time, so that's another 100 diamonds/week on average. (With Perks I expect it'll be 90%-100% going forward, which should balance out any loss in individually-earned diamonds.)
I turn over the MA maybe 2-3 times a week. I've never tracked it, but I'm pretty sure I get 500 diamonds at least once a month. I don't keep Goddesses of Wishes out regularly. As they stack I'll put 3 or so out at once; the small prizes are less annoying when multiplied.
That adds up to an average 900+ diamonds per week. It does tend to be inconsistent, no question: A great week, a couple middling ones, a week of utmost barrenness, et cetera. I started tracking in ch. 5, but IIRC I was getting about the same in ch 4. Maybe a little less because I was still building up my Genie stock.