I think the author has a point, but I also think he is overreacting quite a bit in terms of the impact he thinks this is going to have. I've lived with a 5.5" Galaxy Note 2 for almost 2 years now. That one carries a 720p display and rarely have I felt that the resolution was inadequate. Shrink that down to 4.7" on the iPhone 6 and I fail to see the issue here. Only spec junkies or nearsighted people who like to plant their face in the display when not wearing contacts or glasses will notice the difference.
As for the camera and battery life, we will have to wait until the reviews come out to make a judgement on how big a deal it is. How much of a difference it makes completely depends on what is more important to each individual user. Personally, I need the bigger screen because I use my phone more as a mini computer than an honest to God phone (in fact, I hate make phonecalls with a passion). If that was not the case, I'd probably have picked something smaller. The Note 2 fits in my pocket, but just barely. 5.5 inches -is- big for a phone, not matter how you put it.
In terms of the iPhone 6+ being an iPad mini killer, I'm not so sure about that either. The difference in screen size is huge. I got an iPad mini with retina display almost a year ago because I felt that my 5.5" phone just wasn't big enough to comfortably surf and read on during those 30+ minute train rides. The mini fits in the pocket of my jacket, so it's not that much more difficult to bring with me and it just feels sooo much less claustrophobic to use. As a result, I could probably ditch the Note 2 and live just fine with the 4.7". In short, it works both ways.
