Concepts and theory are certainly critical, but one needs to practice in order to achieve mastery. The conceptual framework for all this stuff is covered in detail in other resources, anyway.
After taking a cursory look around, Edabit seems to be filling a very specific need. I like it.
Apps like Duolingo are just a method for daily exposure on the long journey of language learning.
For example, reading only grammar books isn't going to get you there, either. But doing something every day is possibly the most important part, and Duolingo can help you build a habit.
I see this criticism of Duolingo all the time by people who sound like they think it failed them because they weren't fluent after finishing it. There is no roadmap that will make you fluent without serious, multifaceted effort on your own part, so it's quite weak criticism when one tool doesn't take you end-to-end.
Based on the test results, I was skipped past 23 of the 40 topics I can see in the course. Considering that I've been learning for only three months, that makes the course look a bit short.
When I then tried the next lesson, I did notice some questions repeating, but there was also some variety. So I don't know whether it's possible to just memorize all the sentences without learning grammar.
Based on me trying Duolingo a single time now, I'd now say that the biggest problem is the small amount of topics covered in a course, which limits the vocabulary you know how to use after completing it.
But that's not what the original complaint said, so maybe someone who's used Duolingo 5 minutes a day for several months is still in a better position to explain what the actual problem with Duolingo is.
It becomes more apparent when you realize these apps are not smart. They were novel at one point, and maybe you can pick up a phrase to catch a native speaker off guard.
Duolingo is using humans to translate web content that algorithms are unsure about. This is the same founder of reCaptcha, who uses captcha's to use humans to tell robots about what the robots are unsure of.
Memrise, on the other hand, just takes the "87% most used phrases" and tries to get you to memorize the.
They have zero holistic approach to any of the languages they offer. You will never learn tense, language-specific concepts and rules, idioms that break all the rules, or whatever locals just say.