"I, as a non-tech founder, would never aproach a developer with a "pay you later" proposal. I do exactly what I advised. I pay the developer about 70% of market rate. And he is actually learning a lot with the experience."

You're in a minority if you never approach people with "pay you later". And... 70% of market rate... and people are learning a lot with the experience.... you are hiring very junior people, it sounds like.