Also find myself really learning something new mostly when peeking into other people's code and trying to understand how it works and hacking together working stuff. Even though FCC-like platforms are great and provide practice, it seems that only when you're not doing separate tasks teaching you a particular theme in programming, but rather working through a set of subsequent actions that you need to do in order to make a working prototype do you really start to understand how this or that tool or method works

Yep, tutorials like FCC have their role but you have to make projects to get better. As you say, hacking about with someone's else's code will do the trick.

I discovered SubmitHub from Indiehackers.

Jason has done an awesome job from reverse-engineering a Meteor todo list tutorial into a music submission website without any formal training in programming.

Thanks for the shout, Pete!