Why are BMW's so slow in reality ( specifically 335i )

[Perfectlap]

You're whole premise is off. You titled your question "why are 335i's slow"?
This would infer that a car is "fast" based on a single metric, straight line acceleration.
A proper sports car is fast or slow based on many metrics which are typically decided by a single lap of a race track with a good mix of fast corners, technical corners, elevation changes, etc.

As far as street racing, this is not something excellent Porsche drivers are known for.
More like the pimply faced spikey haired 19 year old in his Civic or the gold chain wearing mullet hair cut guy in his mullet car. I've been challenged by both and it always makes think back to when I was a dummy too.