If you mean current gen, you might be right but the last generation had the Wii U which not only emulated all of Nintendo's previous consoles near perfectly but a myriad of other retro consoles as well.
The Wii U's CPU and GPU were specifically designed so that they include any features needed to play Wii and by extension GCN games, so no that wasnt emulation, its also one of the reasons why the console ended up expensive to make and underpowered compared to the competition.
As for all the other consoles that the Wii U emulated, the Switch is currently capable of running them or alternatives through homebrew or Ubuntu/Android, most of the time or probably always better than the Wii U did since the Switch has a better CPU.
About 3DS emulation on Switch, I think that doing an approach similar to what vita2hos is trying to do would be the best way as the 3DS's CPU features the ARMv6 Instruction Set which the Switch can run natively through its A57's Aarch32 mode.
For the GPU and OS functions, its possible to also do what vita2hos is striving to do by intercepting any function calls and instead calling the equivalent that the Switch has access to.
Ofc this is a very surface level thinking as the matter is probably much more complex, but I still believe good 3DS emulation can happen on Switch even tough the option I suggested isnt exactly emulation.