First of all, I don't know specifically. I've heard the hypothesis that it is essentially an experiment but I've never read anything from anyone who has directly done research there or is familiar with Inca structures around Cusco, and it's entirely possible that no one has done research there in decades so the old idea sticks. So on that hand, I'm not sure.

But reasonable? It's definitely reasonable. For one, I take exception to your claim that the Inca were ancient and "primitive." They were the largest and most complex state to develop in the Prehispanic Andes and they created a massive empire in a very short time, requiring no small amount of logistical prowess, and this empire brought a huge amount of wealth into Cusco. And with wealth comes the ability to build large, complex structures that take a lot of time, expertise, and money to design and build. And the rapid population growth would have brought together experts and ideas from all over the empire, and when large numbers of people come together like that you tend to get ideas that no individual could come up with on their own. And remember in terms of European chronologies the Inca were Medieval and Renaissance, and follow on knowledge and traditions that began over 3000 years before the Inca had even coalesced as an ethnic group.

As for experiments, we call it an experiment for our sake, because that helps us compare that thing to something that we know. People have always experimented with agriculture and cultivation, ever since agriculture began. These weren't scientific experiments in our sense of that term, but they were trial and error experiments to see what worked and what didn't. Moray could certainly be a more sophisticated form of this.

Lastly, you need to understand the environment of the Andes. As you climb from the coastal zone through the intermediary Yungas into the highlands and back down into the Amazon on the other side you get massive variation in what you can grow, even over a short range. This depicts modern crops, but the idea is the same (and it is the best image I have seen for this). John Murra came up with the concept of the vertical archipelago, which basically states that communities owned discrete parcels of land at different elevations in a river valley because they could grow different crops at different altitudes. If you are on the highland plains and you descend just a little bit into a valley you suddenly see fruits and other things that just don't grow even a little bit higher. Moray supposedly uses this to determine which crops grow best at which altitude. And it's not just about temperature, but rather temperature, atmosphere, and wind patterns all play a role. Moray's 30m might not be much, but it can supposedly mimic several environments. I say supposedly because again I am not super familiar with Moray itself, but I am familiar with Prehispanic life in the Andes in general.

One last thing: Inca agricultural terraces were not merely functional, but they were very well built because they served an aesthetic purpose, they were built to represent what an Inca thought a field should look like. Kind of like the difference between a glistening downtown office tower and a red brick one-story business park; both provide perfectly functional office space, but no multinational corporation will be headquartered in a frumpy business park because it doesn't suit the idea of what an office should look like. So this aesthetic sense, especially in the rich lands surrounding the Inca capital (which include spectacular and well-built sites like Ollantaytambo, Pisac, Sacsayhuaman, and yes, Machu Picchu) likely also played a big role in how Moray was built.