Graphics won't matter so Nintendo instantly becomes a high end console.
Dedicated gaming devices might still be used even if it's just for controllers and convenience.
Nintendo seems fine for now because they've successfully predicted the future again.
DS embraced touchscreen and microphone games that were about to become huge thanks to Apple/Android. (DSi added a camera)
Wii was a TV-box with a TV remote as a controller, the market didn't go that way but most new TVs are smart TVs and therefore could easily become consoles. Every TV manufacturer could install their own Wii Sports if they have motion control in the remote.
3DS used multiple cameras and motion control because that's what smartphones were about to come with as standard.
WiiU thought multiple devices would be connected and would allow for streaming, extra screen(s) and asymmetric gameplay. They do but no-one takes advantage of it.
Switch is a 'tablet' (does the Gameboy count as a tablet?) built around a selection of blutooth controllers and TV docking which is one of the future battlegrounds if 5G is as fast and stable enough as promised and/or when the graphics difference shrinks.
Nintendo has and is successfully defending itself against smart devices. Smartphones, tablets, smart TVs, TV boxes. If 5G makes every device a PS6 level graphics beast then the war will be about exclusive software, controllers, friends lists/online, maybe the ability to easily switch between TV and portable, price, simplicity/accessibility, gimmicky addons, local multiplayer.
Sony and MS lose all (except online) their strengths while Nintendo's are magnified.
If we all wake up tomorrow and every $30 Android device can seamlessly stream PS6 level graphics with zero lag and zero cost to porting, who wins the console war?
Don't Play Stationary 4 ever. Switch!