What unfair advantage do bootstrapped founders have over venture backed founders?

If you are a bootstrapped founder you can prioritize the end customer in everything that you do. This helps you to: 1) Reduce marketing cost 2) Gain word-of-mouth referrals 3) Retain customers more effectively

flexibility

Total control.

Complete control, and rock solid determination

Own all of your decisions with no undue pressure from VC's

Autonomy, flexibility, long-term focus.

Independence and not having to answer to anyone but yourself.