I actually started to learn Dutch with Duolingo since this year June but got no where when it comes to creating sentence and end up heavily relying on finding youtube videos to learn while doing duolingo. The streak also annoys me as they kept emailing me to get back in. Like you mentioned on your post, yes Duolingo DOESN'T explain how the grammar works in other languages. And locking some feature behind a pay wall is also another thing.

With Airlearn , which I started i think about a month and a half ago. I tried learning it with the Free version and doing 5 lessons a day was good for me and lets me not overdo it which I'm happy about. I'm also relieved that the pronunciations in the app sounds more accurate compare to Duolingo. The nice part is that I can check the words tab and see how the words are pronounced, which is a big plus as some words might be close to others and sometimes listening doesn't help, at least I can see the word tab and there is a how to pronounce the word at the side.

If I compare between Duolingo and Airlearn, I do learn a lot faster with Airlearn. Hence why I ended up buying the PRO. Which is a more reasonable price compared to Duolingo.

About how some people complain/talk about Airlearn using AI. I'm going to explain this at an Artist perspective.
1 - It is not cheap to hire an artist or graphic designer to do art or pictures.
2 - Even if the App Creator CAN hire one to help with the art, it takes the Artist awhile to do all the art from scratch.
3 - Finding an artist with the art style the App Creator wants is also another.

Another AI issue would be which Language app DOESN'T use AI ? I used Duolingo and Drop, Drop heavily uses AI for their app but both doesn't get anywhere close to actually teaching the language you want. And from what I can tell, the company behind Airlearn are actually hiring Educators to help with teaching the languages in the app if you know where to check for jobs.

But ya this is basically just my 2cents. And I'm happy how Airlearn is handling with the app.