The land size isn't the issue. It's the design.
In my opinion, Super Nintendo World in Japan is a masterpiece of theme park design. It's the best theme park land in the world. I remarked on this earlier, but the land feels like it was designed by video game designers. Stuff is hidden from the "player" using perspective tricks. The land starts with the simpler interactive experiences and gradually builds up to the more complicated stuff. The two levels create depth and scale. Even the smaller stuff is there, like how the paintings in the castle shift images depending on perspective like in Super Mario 64, or how you see the various mini-game enemies on Mt Beanpole when you first enter the land. There's plenty of stuff for people to do without the power-up bands, which give you a reason to buy a power-up band in the first place. Easter eggs are all over the place, from the rides (like the Mario ship from Super Mario Galaxy 2 on Yoshi, OMG) to the mini-games. Everything has a purpose. Unique food, unique rides, unique merch, interactivity everywhere. Donkey Kong will just enhance this experience.
Super Nintendo World in Hollywood has most of the picture, but is missing some pretty big details. You could double the size of the land and it would still be the same way. Random blocks were substituted in for experiences, and it doesn't work. Why should a guest buy a power-up band if they don't know if it's worth it? That's the whole point of the smaller stuff in Japan. 1-Up and Toadstool Cafe will always be crowded, as there's nowhere else for guests to get those items/food in the land. The multi-level experience is almost non-existent. There's no supporting attraction for guests to go to if Mario Kart breaks down.
The experience is still there, it's just missing a lot of the magic.