FI is great for several reasons: 1) It focuses more on developing entrepreneurs, vs. necessarily companies. The requirement that you incorporate to graduate is kind of at odds with this, but definitely the curriculum for the first half of the program is compatible with coming up with an idea and launching it within the program. 2) It's compatible with having a day job during the program -- if you have good time management skills, you can keep the day job while attending FI, launching your company, and thus not have to worry about funding. This is a major differentiator vs. YC. 3) Some of the mentors (IMO Aaron Patzer, Jon Betts-Croix, Ram from A9, and some others) were fucking AMAZING. It's worth $600 just to see their sessions. 4) You have some chance of meeting great cofounders in the program -- I actually met a few people I'd be happy to work with, and have gone down the road to doing a startup with someone from the program.
For the ideal training to do a startup (other than JFDI), I'd do an entrepreneurship program in undergrad (e.g. MIT E-Club, 100k contest), then something like YC to build a product, and Founder Institute to learn about the nuts and bolts of running a company, possibly interspersed with time spent working at either startups or funded former-startups.