Unless, as is often the case in my experience, the hard stuff consists largely of fixing bugs and edge cases in your implementation of the easy stuff. I've seen multiple people already end up forced back to the drawing board because their "easy stuff" AI implementation had critical flaws they only realized after they thought they were done. It's hard to prove counterfactuals, but I'm pretty confident they would have gotten it right the first time if they hadn't used AI, they're not bad engineers.