I agree, not as I use Apple, I lost the fanboy thing. I want to see what the REAL cause was, maybe we wont know. My 6+ is 3yo now, its normal, well it feels normal. If its a help user/didnt tell them, they need a slap. If its to promote sales, make it headline news.
Wait is there some sort of conspiracy on the REAL cause?
If anything it could just be that since the release of 6/6+, they allowed higher/faster charging current/wattage which is known to degrade batteries faster. While the 5s/5 were capped at 5W charging with a ton of people complaining that "crapple is not letting people charging their phone fast enough."
People have observed the same thing on those cylindrical li-ion cells where faster charging degrades the cell quicker and lower voltage from cells with high cycle count. So these are all pretty well known already.
Basically charge your devices at a lower current (the included 5W charger is pretty good). Keep the battery at a decent room temp and charge as often as you can so you are not cycling the cell that much.
eg. discharging from 100% to 0% = 1 cycle count, discharging from 100% to 80% 5 times with full recharge each is also 1 cycle count.
Apparently discharging all the way down to zero causes extra wear on the battery, so I don't think it is quite as simple as your calculation. Apple have also said in their announcement that the chemicals aging in the batteries can impact on the life.