>>38138829Tajiri, Morimoto, Kawachimaru & Unno were all competent. Masuda suffers from George Lucas Syndrome, whomever was holding him back in Gens 3-5 is gone and Masuda's being going downhill ever since.
Ohmori has potential but Iwao is hopeless, Sword & Shield will determine whether Ohmori is just waiting for lightning to strike or if he's incapable but has his moments.
Overall I'd say the downfall would be around Gen 6 when the reigns on Masuda were let off although it could merely be a valley in the overall series if Ohmori can pull it back with SS.