Hahaha Chiara I'm so sorry I wish I had advice but your whole message is... so relatable. I think we all feel like this and I'm not sure it ever goes away.
"Like a lot of artist I would like to achieve awesome result with very little effort" YUP. I love watching concept artists paint an amazing scene in like 30 minutes and then feel frustrated that I can't do that. (Yet, heh.)
And so annoying to spend hours of the little free time I have on something and it feels like A. I'm just working more, after work, and B. it doesn't even turn out good. Worst.
...But nothing really to do about it except [complain and] learn from it and hope it goes better next time.
I also disagree with "practice makes perfect" — yes it does but if someone is just repeating the same steps again and again, they might be perfecting bad habits. It's more efficient to dissect what works in the art you like. Really take it apart: pick out the techniques/ideas/etc. you're drawn to, and then incorporate them in your own work. Don't worry about copying; in the end the mixture of different things you've chosen to include + your own natural habits will make it your own.