You’re right insofar as objectively the 2017 models have a lot of features the 2015s don’t, but as I noted I was referring specifically to people intending on general mixed use (as per the OP) - who would likely benefit more from legacy ports, including USB A, SD card reader, HDMI and MagSafe over a professional who might benefit more from investing in new accessories that can leverage the benefits of USB C. The power is less of a factor for the mixed use scenario and as long as you don’t need a dGPU the 2015 is still just about as powerful as anything else out there to all intents and purposes.
The 2017s do benefit from being cooler running (and indeed don’t exceed their power supply capacity when running at full tilt which was a problem, certainly for the dGPU equipped 2013 and 2014 models, and I assume the 2015 with dGPU as well?). As far as the keyboard goes, that’s kind of something you just have to understand might be a problem when you buy it - you just need to be aware you might have to be without the machine for a week or so if you do experience a key failure. As far as general mixed use typing goes, the experience is fine.
I’d also note the 2016- models are noticeably better in terms of portability (something I was initially sceptical of from the comparison pictures that seemed to show little difference) and this is probably the main draw to me as the 15” feels closer to using a 13” MBA with all the benefits of the larger, sharper screen. If they could nail 12h realistic light usage battery life and fix the keyboard (and lower the price a little) I think it would probably take the mantle as the most compelling machine Apple has to offer.