This is surprising to me, and I'm getting confused. A hybrid that you don't plug in, clearly gets better gas mileage than a gas car, so must cost less per mile

This is surprising to me, and I'm getting confused. A hybrid that you don't plug in, clearly gets better gas mileage than a gas car, so must cost less per mile? (Or is the original research amortizing the more expensive original purchase price too?) But does that mean that "traditional" (not plug-in) hybrids are cheaper to power per-mile than either full ICE or full EV? That seems surprising too. (And then what about plug-in hybrids?)