I've played the piano for about 3 years now, took lessons for the first year of that then stopped. Using pianomarvel.com worked pretty well for me for a while for learning certain skills. I had already taken some lessons, so I wasn't completely lacking instruction in basic technique, but I was poor at reading music (let alone sight reading). My reading skills improved significantly over a few months of doing most of their course, which basically just has you plug in your keyboard by midi to your computer and then play along to songs until you get it nearly correct. If I had been self-studying, I wouldn't have been exposed to as wide a range of pieces (more even than when I was taking lessons). I'm now much more confident picking up a new piece of classical or modern music. So, I'd say that "apps" are still useful. (Though you definitely need one that uses a real keyboard or piano and not a tablet touchscreen - bleh!) Had I been more dedicated, I could have used it to practice chords, scales, and arpeggios too.
Not sure what you mean - are you saying that the program wouldn't have provided motivations for the structure of chords and so it would have been brute memorization? That's pretty likely. It had very minimal instruction in music theory, and actually the program is more marketed at instructors to give their students structure to their non-lesson practice time and add some gamification to motivate young (and not-so-young) learners.
