It’s not vertical integration it’s that’s they have significantly less bureaucracy and overhead compared to legacy companies. That advantage won’t last forever but for 10-20 years it will propel them ahead
Tesla also benefits from horizontal integration, sharing a common charger module between vehicle and Supercharger. This improves scale and cost.
They had very little capital, and they knew that they couldn't sell cars without a charging network. So they put all their efforts into reusing as much as they could from their high volume cars to improve economies of scale.
Noone else had the same incentives. That part is changing fast, though.