Knowing the chip designer tells you nothing about its performance. I'd *hope* something so much newer would look down on the Vita from a mountain, but just knowing it's Nvidia isn't proof of that.
Actually, it sort of does. The only two architectures used in Tegra thus far which support Vulkan are Kepler used in the TK1 and Maxwell used in the TX1. In the case of Kepler, the TK1 is actually the smallest possible configuration (1 SM, 192 "cores"), and even clocked down to absurdly low levels would significantly outperform the Vita. The TX1 uses two Maxwell SMs (each 128 cores), so would be able to be chopped in half, but again even half of the TX1 clocked extremely low would still outperform Vita by a massive degree. A Pascal-based Tegra could in theory be produced with just one SM (64 cores), but then you're on 16nm, and even the most stringent TDP imaginable should be able to get a reasonable clock out of it.
No, but that isn't really a great analogy. Nintendo's consoles have been trending down for a while, and now you will give consumers another reason not to get it. You certainly cannot assume that if it works for the iPhone/iPad, it will work for Nintendo. If what you predict is true, the amount of people who want to play their NX handheld games on a TV so badly that they would pay an additionally ~$300 will be less than the amount of people who got a Wii U IMO.
You're assuming everyone's happiest playing games on a handheld. Some people want to play games on a handheld, some people prefer to play them on a TV. Nintendo would accommodate both while giving them the largest possible games library by releasing a console and handheld which share the same library.