Performance+Android+Google play store+sideload yes emulators.
You can install RetroArch on any Android device it's free and has NES, SNES, Genesis, GBA, GBC, Arcade, N64, PS1, etc. all from one menu.
Smart TV streaming apps usually get pretty glitchy in 4 years or so. Also they often have a limited app library. If buying a new smart TV you probably can wait a few years to buy a streaming box, as long as the TV has all the apps you want.
Yeah you can use emulators with a tv box. An advantage of a box is you can always upgrade to a more powerful one a year or few later. But if you pay more for a smart TV or rely on a smart TV's android it may eventually stop getting updates and features.