Not disagreeing, but why is that??
Duo lingo doesn't have a grammar course beyond tapping on the words to look at their meaning, this app kinda needs you to have some sorry of basic knowledge of grammar and sentence structure.
Hm... I don't catch your meaning well... Anyway I do not have a problem if Duo wants to teach conversational uses only and there must be people out there who only want to learn how to talk. I only think it is important for learners to know what they are learning.