Looks like this game still had a monstrous effect despite being a parallel series to the main branch
"Thanks to Famitsu, we now have sales data for Pokemon: Let’s Go, Pikachu and Pokemon: Let’s Go, Eevee in Japan. In its first three days, the two games sold 664,198 copies. This figure accounts for physical copies, download cards, Poke Ball Plus bundles, and Switch bundles. Digital sales are not included."