Defensibility re: companies is well studied, by Hamilton Helmer who and his grad student did case studies of several hundred "defensible" companies and identified 7 "powers" that help companies defend against specific competitors. Note that each power is only applicable towards a specific competitor, and not as a blanket statement. The powers are 1. economies of scale, 2. network effects, 3. counter positioning, 4. Switching costs, 5. Branding, 6. Cornered resource and 7. process power.

I highly recommend Cedric's writing on the topic (behind a paywall) https://commoncog.com/7-powers-summary/