It seems that your definition of efficiency is heavily lopsided. My understanding of efficiency is entirely economic, i.e. I don't care about power consumption and hashrates as such. All I care is the balance of costs and revenues. In other words, the miner that incurs less cost and brings in more revenue is more efficient (i.e. does more with less) than the one that does the opposite...
That's what all technical parameters ultimately boil down to
my definition is different, talking about the initial investment as efficiency is a no-sense, the efficiency is only related to consumption, and the s7 consume half of the s5, so x2 efficiency
The problem is it doesn't in the least guarantee that with an s7 you will profit twice as much as with an s5 given only its half as much power consumption. Initial investment (aka capital expenditure) as a part of fixed costs defines your break-even point. You still have to shell out on the equipment first, whether you love it or not. Your personal opinion (lol) that you can sell your miner is not related to this, and I highly doubt that you will get for it the same price which you bought it at after a few months of operation (and more so before the halving)...
Even if you
personally will be lucky to sell your device at its original price tag