What's missing from AI-powered language learning apps?

I've been building TubeFluent, an app that turns YouTube videos into English lessons — inline word lookup, AI speaking practice, pronunciation scoring down to the phoneme level, and a 5-dimension growth tracker (listening/speaking/reading/writing/vocabulary) instead of a simple streak.

Before I launch, I'd love to hear from people who've tried other language apps (Duolingo, Trancy, etc.) — what's the one thing that made you quit, or the one thing you wish existed?