Let's look at it this way:
We expect the four worlds to be -
A World of Play (Nintendo)
A World of Dreams (DreamWorks)
A World of Magic (Fantastic Beasts)
A World of Monsters (Classic Monsters)
Nintendo, we know, includes at least 2 lands (Mushroom Kingdom and Donkey Kong Jungle), that may become 3 with Yoshi's Island. Regardless, that includes three rides and at least one play area.
DreamWorks will likely have at least 3 lands, and maybe 4. Each land will likely have at least one ride (maybe two in a couple). At least one land will include some sort of play area.
Right there, we can assume seven to ten rides/attractions.
Magic and Monsters I expect to have at least two lands each (somehow), with one to three rides/attractions in each. Minimum expectation, we have 12 rides/attractions. That's a full day park. Even LOW expectations of 10 rides is a full day. Hopeful expectations puts an average of four major attractions a world, so 16.
That feels... Accurate.