The issue with this is that it breaks the entire premise of the Switch, which is that you can play games on the go or on the TV. Any game.
If only the dock is improved, they'd either have to spend a lot of time (and money) making lower quality assets and graphics settings for portable mode, or make docked-only games. Which kinda goes against everything the console is about.
Sure, they should improve handheld mode as well. But handheld will always have a downgrade in comparison with handheld + docked. I don't see Nintendo having a portable videogame that is alone as powerful as a PS4/XO in next gen, at least not using their current low-price police. They need the dock to an extra supply of raw power
I understand having docked-only games is a issue, but they don't need ALL their games to be docked-only, only the fewer games where the portable mode alone can't run (probably some engine-specific 3rd party games)