I consider the PSP a handheld, but I consider the PSV a portable console.
The Nintendo Switch, being larger than a PSV, should be considered a portable console in my opinion. It may look like a handheld device, but it is really just a tablet with beefier specs.
While there is a distinction to be made between a portable and a handheld, your definitions are all over the place.
A portable would be something that you can easily carry about. A handheld is something you can play while holding in your hands. By definition all handhelds have to portable, but the converse isn't true. A laptop or a gaming tablet is portable but not handheld.
Whether you can carry or fit in one hand or 2 does not matter, people don't carry about their things in their hands, it's either a bag or their pocket. Some handhelds like the 3DS XL don't even fit into a pocket. None of the handhelds can fit in one hand except for the Gameboy Advance SP (folded) or the Gameboy Micro.
Since you hold the Switch in your hands while playing, it is a handheld. You can also play it as a non-handheld portable, propping it up with the stand and using the Pro/Grip controller.