>>35709866The Japanese equivalent tweet doesn't say anything about them being "core" titles, it just says they're the newest game in the Pocket Monsters series. The Japanese conference slides slides refer to the 2019 game being a 本編 game, but not Let's Go.
If anything, they're sort of both core game and spin-offs at the same time. They use the Pocket Monsters title that main games use in Japanese, rather than the shortened Pokemon title spin-offs use, but it isn't considered a mainline (本編) game like the other Pocket Monster games.
