Practice makes perfect?

I am (after 10 years) a beginner pianist who wants to improve. I practice, but not diligently enough. On average I think I practice 5 days a week, for about 1/2 hour, so that's less than 3 hours a week. Clearly I could do better. But I am proud of the effort I put in and I definitely have made a lot of progress. But I am at best still an advanced beginner.

From an article, "If you're busy, you're doing something wrong",

"We can start by disproving the assumption that the elite players dedicate more hours to music. The time diaries revealed that both groups spent, on average, the same number of hours on music per week (around 50).

The difference was in how they spent this time. The elite players were spending almost three times more hours than the average players on deliberate practice — the uncomfortable, methodical work of stretching your ability. (from: "If you're busy, you're doing something wrong")