It works for some people, clearly, as stated by some on this very thread. I hope you will not move from "Duolingo is useless for everyone on this earth" to "anyone saying Duolingo is useful for her/him is in denial"...

The issue here is that what you wrote is just not true. I did Ukrainian for a year. I started to be able to understand some of the content around a year in. I started to be able to parse Cyrillic.

I did tried other apps here and there, but none of them stuck for more them two days. Overwhelming majority, like almost all of what I learned is from Duolingo.

The progress was actually very real, painless and fine. I did not expected to be fluent. I improved more then would be possible without it.