I'd agree with most of this, but I don't think I'd argue they were ever replaced by anything else, just that the use case is too narrow.

Tablets are generally larger, have flappy keyboards if keyboards at all, are way more expensive, don't have a built in mouse and often don't support mice well, and they run a mobile OS, not a desktop OS. They are very different products solving very different problems. If you argue netbooks were just for playing movies, sure, but that's not how I viewed them at all, especially since there were portable DVD players in the same form factor available for many years before netbooks existed. If that was the use case, there'd be no reason to run windows or have a keyboard.

I don't see how they replace a large phone at all - a large phone is a much smaller screen and fits in your pocket. And makes calls. And is a touch screen. And has mobile internet access. They're no where near the same thing.

Ultra books I think is the closest "replacement" here, but I'd argue it's more of an evolution and/or a hybridization with a regular laptop.

I'd actually argue Chromebooks were the killer here. They still take notes well, are portable, cheap, have first party mouse support, are generally smaller and lighter weight, and are more type-able than both netbooks and tablets.