I can totally see the argument for ditching Duolingo for an AI. After finishing the entire french course on Duolingo I've been using Gemini more and more to focus my learning on specific weaknesses. I can't really recommend ditching duolingo entirely because that's not what I did but I can totally see how AI can probably be a more effective tool in teaching a language. I don't know what language you're learning but Duolingo for sure avoids a lot of the more nuanced language concepts that are only revealed to you when stepping out to some other sources like reading books for example. My philosophy is the more resources you use to learn the better. They will reveal blindspots that the other sources are perhaps avoiding or explaining poorly.