Not at all. You act like 720p and Tegra X1 are a big deal when the former is a resolution that has been standard among portable devices for close to five years and the latter is one of the few chipsets that make sense for a gaming-focused portable with support for the latest engines and tools. In fact, I could just as easily say that they're using that chip because there will be multiple devices, and X1 would give their whole ecosystem a higher baseline.
For reference, the 3DS launched with 240p
5 years ago... when you claim 720p was already becoming the standard. Nintendo has consistently been far behind the curve with their handheld screens with only meager jumps in resolution each gen, and the idea that they're suddenly going to jump to HD for a dedicated handheld just for the sake of having it doesn't make sense to me. They're not going to drive the costs up and make a more expensive device just for the luxury of having an HD screen- this company has made it clear that they don't do things like that. If NX is going to include a console, I'd expect the handheld to be a little more modest. It could still run console games with a 540p or 480p screen, for instance.
And if they're going to have a dedicated console... why bother connecting the handheld to the TV at all? Why put so much emphasis on using the handheld as a console if they're going to specifically design a console to perform that same function and play the same games? Wouldn't it undercut that hypothetical later-releasing console's appeal if the handheld could already give people that same function? The only real need to buy the console would be more power, but again, Nintendo is absolutely not the kind of company that caters to that kind of thing.
I'm not saying it's impossible, I'm just saying it doesn't seem plausible that Nintendo would shoulder the extra expense and release a high-powered handheld that can function as a home console if they were also going to release a console dedicated to doing that same thing. If they're going to have two systems, why not keep them as focused and cost-efficient as possible? Why so much unneeded overlap?
If you mean a NX handheld and NX console combined would cost less than a NX hybrid device, that seems very unlikely given the fact you're using twice as many parts and other materials. I know it's easy to say they should have gone for separate cheaper devices, but isn't it possible they looked into all the scenarios and have projections that determined this is the cheapest route?
If this thing comes in at even $350 (unlikely), it's still cheaper than Wii + DS and Wii U + 3DS.
But the point is that not everyone needs both devices. In Japan, the handheld is clearly the more important system. In the west, the console will probably matter more. Part of the appeal of the NX (as I was anticipating it) was that it would solve those kinds of regional problems by letting people choose whichever form they prefer by making the form factor unimportant; the same software sells either way, so Nintendo could afford to mainly just push a handheld in Japan and let the console stay in the background. They could do the reverse in the west, although handhelds do pretty well here.
If the same software is running across both devices, I think the number of people who would want to buy both would decrease sharply. I have a 3DS, but I mostly play it at home. I just like it for the games. If I could play all of those on a console, I'd probably not have bothered with a portable.
Why force everyone to pay a higher price for one device when people could buy a cheaper system better suited to the type of play they want?