1. Every new generation of Pok?mon has a weaker soundtrack than the previous.
2. Which also means the 1st generation Pok?mon games, as well as Pok?mon Let’s Go, have the strongest soundtrack.
I think it's a mixed bag. I think that the first three generations had strong OSTs. Then Gen IV was like suddenly completely forgettable. Gen V had a few great tracks. Gen VI, IMO, was excellent. Gen VII was back to mostly forgettable, and sadly, Gen VIII seems to have followed that trend.
If anything I would say that the series' music really bottomed out with D/P/Pt. Most generations since haven't been that great, either, but at least I can say I remember some tracks from them. Literally the only track I remember from D/P/Pt is Route 209 and that's only because it reminded me of ELO's Telephone Line, which played on a radio station I listened to during the time I was playing through Diamond.