Would it have been better if Apple had released an iPhone 6C as an upgrade to the popular iPhone 5C in lieu of releasing an iPhone 6 Plus? If so, why, and if not, why?
No I don't think so. Looking at the acceptance of the larger iPhone model it's clear that folks wanted the larger screens. Although there are no formal numbers that I'm aware of, anecdotal evidence would suggest that the Plus has been very well received. There was a recent post in the blog that showed a graph which depicted an inverse correlation between Samsung sales and iPhone 6/6+ sales. End users want larger screens.
And that's what I'm getting in Seotember.