Tiniest Eternatus. But to be fair, in Sw/Sh, the sprites oftentimes do not match the Pokedex entries.
The scale of a lot of pokemon in the Pokedex already are nonsense. Pikachu, for instance, is routinely shown as being half the height of most characters, while in the pokedex, it's supposed to be about one foot tall (and I seem to recall it being listed as smaller in Gen 1, before the anime). That's before we go with all the "I can have my wailord follow me into the pokemart through the sliding glass doors out front" or insect-sized pokemon being presented as less than an order of magnitude smaller than said wailord in-game.
The series rightly ignores the Pokedex's gibberish routinely, since most of it defies all logic or has horrific fridge logic implications.