For example, I'm pretty poor at slap bass but there are no lessons which cover it. I have found at least one song where you slap (level 10!) but how can I practice to get to the level? Also, time signatures - again, I found a song in 5/4 but what about lessons covering this and exercises to build you skills. What about tapping? Harmonics?
Don't get me wrong, I like the app but having paid for a subscription I don't just want more and more songs, it's got to keep pushing us a players to master other skills