I write fantasy ala Tolkien (my aspiration, not my achievement) and I agree with your take on simple plots. Complexity can develop elsewhere, in the motivations and even distractions a character experiences. It has a way of arising on its own. In the theory of emergence, complexity is a function of decentralized systems that produce it naturally and the singular mind of a novelist is not terribly decentralized. I would apply what you said above to poetry, as well. We have a writers' group on Discord if you'd be interested in checking it out. That's where I'm currently workshopping my novel, which is about a war in medieval Ireland that's financed by debt through a central-banking faery who writes poetry. But I swear - the plot is actually pretty simple. 😃
https://discord.gg/8bEWsdW
Tolkien’s approach to writing a story is quite unique. He created the world in which his stories took place in first, which meant that the plot of each story was another chapter in the history of his world. Some may take this as a “make it up as you go along”, but Tolkien allowed a lot of the story to write itself thanks to his in depth world.
Financing war with poetic Faery money is not a premise I have ever heard before and I hope that you are successful with the final product.