If a professional developer can't understand bitcoin, then i would doubt about his professionalism, i mean, I'm a developer but I'm not a professional and i understand bitcoin, it takes me some time and the code level still not clear at all for me, but it's clear to me how it works.

There are books like "Mastering Bitcoin" if any developer reads it it will be easy to understand how it works. Don't try to understand the code, just follow the logic.