I'm saying that Techstars has only had 5 years to refine itself. HBS has had over 100. I would think by that definition alone HBS should be churning out better results!
Is HBS designed to produce tech startups though? HBS is probably closer to their desired results by virtue of "refinement" of it's aims and processes, yes. However unless those aims include "creating more tech startups" I don't see how their longevity is especially relevant.
If Harvard is better at producing startups than TS, regardless of the reason (alumni, experience), then Harvard would actually be a better choice than TS for someone looking to found a startup.