Amusement parks during rainy season

I've been sharing ideas of things to do during the rainy season in Japan. One place that won't make the list is amusement parks. They are the main place I avoid during rainy season. HOWEVER, there are some amusement parks that might be worth considering for the rainy season in the Kanto plain. Including, Tokyo Disney Resort. 

The reason I wouldn't take Tokyo Disney Resort off the cards for rainy season is because a lot of it is actually under cover. Moreover, some of the rides are 100% indoors. I would like to say that it is less likely to busy during rainy season, but these days Tokyo Disney Resort is busy all the time. However, in saying that, it often is less busy on a rainy weekday. But rain also means that some of the outdoor entertainment, such as parades, maybe cancelled. 

Rainy season is worth considering as a time to visit Sanrio Puroland as it is indoors. However, Sanrio Puroland is more a theme park than an amusement park really. But it does have some amusement-style attractions. However, its more of a themed experience overall. Tokyo Joypolis is another indoor park in Tokyo and it does have VR amusement rides. Legoland Discovery is also indoors... the list goes on. The thing with indoor amusement parks though is that they will actually be busier during rainy season as a lot of people have the same idea to avoid the rain! 

Have you visited an amusement park during rainy season? Was it busy?