Have to take a better look but IIRC he differentiates between climates. How would that justify let’s just say California?
Either way, there is lots of Rishonim to point to for justification for Shmini Etzeres. There is no such thing for making a bracha while it’s raining. Are there any sources for that at all? Not to mention people who aren’t on the spiritual level to claim they are unbothered by the downpour?