If the easy things are done faster you xan spend more time on the hard stuff. No need to spend 2 hours on making the UI for the MVP when an AI can make a decent UI in 2 min. Means you have 2 hours more to spend on the hard stuff.

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.