YC doesn't teach you the fundamental skills of programming that you need to become a software engineer. A lot of people don't want to take a risky shot at being a successful entrepreneur. They would much rather have a stable job paying them a six-figure salary. That's one career track that a traditional CS degree provides. If that's your goal, YC isn't really the right way to go. You are much better off going through Lambda School.
However, let's say you have some experience as a software engineer, but you are interested in having a more flexible career, and not just writing code, but also getting more into the "business" side of things. You're willing to take a little financial risk for a more interesting career path. One option is to go back to school and get an MBA. But YC is really a good alternative here. You will learn a lot about business, even if you are the "technical cofounder" and spend most of your time writing code.