There are some topics which kwiziq is very picky about. One such, in my opinion, is the differentiation between beaucoup de and de nombreux (another one is the meticulous distinction between aimer bien and aimer beaucoup). Yes, there is a difference between them, but it is small, often relative to intonation and situation, sometimes also dependent on regional preferences. These finer points of language usage are taught at a level where many learners still struggle with basic grammar concepts.

 I wonder if there shouldn't be a separate category of lessons dedicated specifically to language use, idioms and "how to really sound French". Then it would be clear that those are at a different level as the other hard core grammar lessons.

There are a lot of things that could potentially fit here and would be fun to master. For example, the many phrases using en and y that are ubiquitous in everyday French (ça y est!, allez-y, j'y suis, s'en vouloir,  s'en sortir, etc.). There are also useful and numerous idioms that lend color to one's French.

Another wild and crazy idea would be to have kwiziq lessons on dictation/reading/listening exercises. They would focus on specific vocabulary and turns of speech used in the corresponding lessons. Learners would have the option to do the lesson first, getting acquainted with the vocab and phrases before doing the exercise. These lessons could also be part of the "how to really sound French" category so as not to clutter up the main thread of grammar lessons.

Or just the distinction between aimer, aimer bien and adorer. J’aime is used for lots of things, but not indiscriminately with people. 

And yet “words” like super and hyper that the académie expressly advise against using, and are listed as prefixes but not words in Larousse,  appear as words in the translations ?