Well, when the s7 came out, it was not overpriced
Let's calculate a bit...
S7 B1
was 1823 USD
In the middle of september 2015 price of BTC was ~230USD that means B1 costs 7.92BTC
At the end of september difficulty was 60,813,224,039 at 4.86Th that translates to 1.206 BTC/month or 6.5 months of ROI with free electricity and zero diff increases - this is a guaranteed non ROI numbers.
That means your analytic skills sucks big time, sorry

My single frustration is about bitmain lowering the price for the s7 to half of what I paid less than 3 months ago.
...
I truly could not sell my batch 7 or 8 miners at a breakeven at the moment, even if I factor in how much btc I've made in the last 60 days, because they're still selling units.
so you included resale value to your ROI calculations? that was a mistake...
When has bitmain ever lowered price by 50% in subsequent batches of miners in less than 60 days and kept selling batches in the past? In my experience, antminers usually sold out quickly, and there was a limit to production. They kept price consistent. The other antminers didn't decrease in value by more than 50% in less than 60 days, like what's happening right now.
bitmain made a huge markup on a relatively simple piece of electronics, it was clear such price won't last long