>>36977155Scenario writer 1 (Tajiri): RGBY, GSC
Scenario writer 2 (Matsumiya): FRLG (credited to Tajiri because is mostly reused dialogue), RSE, DPPt, BWBW2, XY, SMUSUM
Scenario writer 3 (Masafumi): ORAS
Trying to fit these games in the same canon or trying to combine them doesn't work because Game Freak writers don't communicate with or ask input from each other. SMUSUM artbook states it's been 2 years since BW2 (and XY because writer said these two take place at the same time).
We still don't know who wrote LGPE, but considering development is happening at the same time as Gen 8 like how Gen 7 was being worked on while ORAS was released, Masafumi Nukita quit, and Tajiri doesn't work in production anymore, it's probably none of them (but may be credited to Tajiri for the same reason FRLG was).