I've owned the 4s, 5, 6+, 6s+, and now the 8+. Never had a problem with the 4s, 5, 6+, or my 6s+. My wife, however, did have the bad battery on her 6s+. We'd do Ingress and her phone would shut off, at first, a few times while walking in the park. Then at the end (before we took it in), her phone would reboot 4-5 times while doing ingress in the park.
The question isn't why does Apple sell processors that are too power hungry, the question is, why didn't Apple fix a known issue in some of the 6s and 6s+ phones' battery? They tried with a 6s replacement but my wife's 6s+ obviously had a problem. Apple did diagnostics but told us her battery was "green" even though it only lasted half a day and would shut off with heavy usage.
My 6s+ had no problems (from 100% to 0% even with heavy CPU apps) and the MAJORITY of 6s+/6s users probably didn't either. Doesn't mean there wasn't a problem, because there was - as seen by the 500+ reddit thread, my wife's iPhone 6s+, and Apple finally acknowledging that in the 6, 6s, and 7 models there were batches of bad batteries that would cause the phone to reboot if too much demand was placed, so they downclocked the CPU (horrible horrible decision, even if it did save them millions upon millions imo).
Honestly think that if Apple had implemented this $29 replacement plan earlier when they started having these problems, instead of downclocking the CPU - more people would have been happier and we'd all view Apple in a brighter light. That said, I think Apple finally doing this is great - sure they could have gone further but you don't stay a profitable company by giving away stuff unless you have to.