Pokémon Sword & Shield have been criticized for using character models that seem to be recycled from the Pokémon games on the Nintendo 3DS, but this is will not be the case, as Game Freak is claiming that the character models in Sword & Shield were built from scratch.
Pokémon Sword & Shield won't be including every Pokémon from throughout the series, due to time limitations, which means that only Pokémon from the Galar region will be included in the games. There are currently over eight hundred Pokémon in existence, which means that it will become increasingly difficult to add all of them in future games. It's for this reason that Game Freak is limiting the number of Pokémon in each game, starting with Pokémon Sword & Shield.
A lot of fans have accused Game Freak of reusing models from the previous Pokémon games on the Nintendo 3DS and there are plenty of comparison videos online to support this idea, as the animations used in Pokémon Sword & Shield are mostly identical to the ones from Pokémon Sun & Moon. According to Polygon, representatives from Game Freak refuted this notion in a Famitsu interview in which they stated that the character models in Pokémon Sword & Shield were built from scratch.
The fact that Pokémon Sword & Shield are appearing on the Nintendo Switch means that the mainline entries in the Pokémon series are transitioning to a home console for the first time, which means that there is an expectation from fans concerning the quality of the graphics. The previous mainline Pokémon games were released on portable systems, so no one expected cutting-edge graphics or highly-detailed character models, but the Nintendo Switch is a far more impressive machine than the Nintendo 3DS, so the expectations for the graphics are higher than ever.
There are likely people who will still refute the claims made by Game Freak concerning the character models, as there is a lot of compelling video evidence to suggest that the models from Pokémon Sun & Moon have been reused. These videos are based on footage from trailers of the games, which means that a more comprehensive analysis won't be made until the games are released.
Pokémon Sword & Shield will be released for the Nintendo Switch on November 15, 2019.