How do you know that the Model 3 doesn't have as stiff a frame as the M3 or M4, or various Porsches? Unless they've all been tested by some independent group, I don't think you can really know. Also, why do you think the M3 or M4, or Porsches in general have a superior suspension? I do agree that Teslas don't make the best track machines, but not because of chassis stiffness or suspension relative to their competition.
Yeah, did Munro say that the chassis was way over-built and too stiff?
Edit: Yep: Another Tesla Model 3 Teardown Highlights Strengths & Opportunities For Tesla | CleanTechnica
Munro said. “They don’t do a good job at part count. The weights are too high. The body is much too stiff.”