The Mercedes E-class is monocoque, like almost all cars. They build the body/frame and then add the powertrain and wheels. Here's the body/frame and the powertrain/suspension coming together.[1] The powertrain and suspension aren't self-supporting; they're a collection of parts held in a fixture. That's very clear in the video of the parts coming together.
The Tesla Model S, though, is body on frame. If it can sit on its wheels without a body, as the Tesla Model S can, it's body-on-frame. Here's the Tesla Model S platform sitting on its wheels, with the powertrain installed.[2]
So is the Tesla Model 3.[3]
[1] https://youtu.be/lPKnM9vC6V0?t=395 [2] https://www.youtube.com/watch?v=l8WUIkD7xxI [3] https://jalopnik.com/why-tesla-needs-to-sell-the-model-3-wit...
If Tesla is stuck on a battery bottleneck it's just as silly as if Mercedes were stuck on a sheet metal bottleneck. Yes, you need reliable component suppliers that can scale with you as you grow and provide the quality you need. If you don't have that, you have a big problem that vertical integration isn't going to solve.