Too Long; Didn't Read
VCs don't think about leaving their VC firms to launch a similar startup. Stealing ideas isn't an option for VCs. VCs won't just spend 3 years getting a patent for an early-stage startup's idea. It takes months for startups to research, build a minimum viable product, fix bugs, do customer development, find the first clients, and actually make money. The probability that the copied idea will be better than the original is lower than your chances of becoming a unicorn.