There are a lot of costs to operating a service center and managing customer deliveries that aren't necessarily considered in gross margins for Tesla whereas they are considered in the case of a traditional automaker in a dealership model. I wouldn't be surprised if Tesla still has an advantage compared to manufacturer+dealer but we won't learn that from comparing vehicle margins directly.

There's also a lot of super weird dealer kickbacks behind the scenes that can make gross margin misleading for traditional autos, probably in Tesla's favor.