I think you'll find that many of the difficult problems in this space worth solving require a great deal of domain specific knowledge, expertise and specialized apps for dealing with it.

For example: I'd like to find Chinese listening material, that is at my level, with pinyin and character subtitles, that follows a certain word repetition strategy optimized for listening learning. Plus, it needs to be able to playback at a fast speed and not too fast speed.

there's a lot of chinese audio podcasts out there but finding one that's exactly at my level and entertaining is challenging. Some apps do it really well, like "immersive chiense" but they need more material. Du Chinese is also a great contender but there's no word progression to the audio, so any listening you do, even if it's intermediate, contains words from HSK 5 and beyond. then those words aren't repeated for a long time, which means you have to repeat the same dialogue many times.

And those are the 2 best Chinese listening apps out of 100s of crappy ones.

the point is, these problems are complicated.