"I think we might need to differ here a bit between learning and helping. As a junior you should get as good as possible through learning."

Sorry, perhaps I'm missing the point you're trying to make, but I don't see how working on real world projects isn't learning?

"You're never learning as much as if you copy the big ones and figure out, why they did stuff they did the way they did it. Because their solutions are already there."

My main issue with this thinking is that you don't know what the problem their solution solves in the first place. Is it user retention? Performance? Branding? Is the solution they're using just the one their budget allowed for? Without being on the inside, you have no way of knowing this.

For the record, I don't think spending time reverse engineering existing solutions is inherently bad. It's a good exercise to learn the tools of the trade, but really thats all it accomplishes. Hell, it's how I learnt all those years ago, trying to copy Carson, Vignelli etc... But again, it was mostly a way to learn the tools, as without being aware of the problem they were facing or trying to solve, how can you know they did? It would be a different story if these redesigns were taken from simply being mockups, and built out into full functioning app/sites/products that fill a particular need, but they're not.

Again, I don't think, and never said that redesigns don't teach you anything. I just don't think they teach anywhere near as much as working on a problem first hand. And besides, Spotify and friends don't need the help.

"But it helps you getting better. I like it more as a way to learn, than "helping" non-profits. Learning while trying to help can be problematic - but I might be too puristic here.""

I see what you're saying about inexperienced "help" being problematic. I agree somewhat. I do agree that sometimes an inexperienced person "helping" could cause more harm than good.

I do design and web work with a few not-for profits who constantly seem to have offers to help. Always from well meaning people, but more often than not, they come with a particular set of ideas and things they can offer, mostly to benefit themselves. But ultimately they get in the way, or don't offer any material benefit to the organisation. However those that take the time to reach out and spend the time actually finding out what problems the organisation is facing, and how they can then use their skills (developing or otherwise) to assist, is in my eyes a much more beneficial exercise for someone trying to get better in the long run.

Design can't happen in a vacuum. It needs to solve a problem. Designers need to work with people, navigate the real problems they face, have the awkward discussions that will inevitably come up and spend the time doing the work that solves those problems.

Edit: Sorry. This reply ended up being more long winded than I originally intended.