To some extent I agree with the critique. Would I be able to write an assay like the op in Italian? surely not. Is their marketing annoying? yes, very much. Is the platform perfect? far from this. However - after 3 years with Duo I am capable of having causal, simple conversations, I can navigate most of the websites in Italian, I understand most of the marketing emails, I can write simple emails myself. I trust this is mostly due to DuoLingo - building the vocabulary and quickly recognizing the patterns (and It was not super simple, my native language is Polish, and I was learning Italian via English interface - there was no Polish-Italian course back then, now there is one but it's just very low quality).
Duolingo helped me build a habit, knowledge of words and patterns. During the 3 years I've spent with the platform I made trips to Italy, I tried talking to people, tried to read texts and and explored some grammar myself. About a month I go feeling I've outgrown the platform I started doing 50min conversations on Preply platform and I am now confidently moving into stage where I can build longer sentences, use past and future tenses and irregular verbs.
In my discussions with friends I emphasize that IMHO Duolingo alone is not going to teach you (complete) language. If you have a goal to learn a language (in general, not on Duolingo) and you use it as one of the tools - it could be really helpful.