Trains in Berlin's public transport go up to 90km/h and don't wait at traffic lights. I bet there's plenty cities with faster public transport, but probably few that can provide near perfect last-mile coverage in the entire metro area. If you want to go fast especially during rush hour, that's an option.
Whenever I've tried picking two random points in Berlin on Google Maps, averaged over all the point pairs I chose, public transportation takes an average of about 50 minutes regardless of physical distance.
If both ends happen to be right by the same line then you can do better, of course — connections and stop distributions are what drag things back to that value.
My old apartment and employer were 8 km apart*, Google says 48 minutes by public transit, 28 minutes by car, 30 minutes cycling, for average speeds of 10/17/16 km/h respectively.
Public transport has a huge cost advantage, it lets me learn the language during my commute, and it's a huge space saver relative to personal cars, but it's nowhere near as fast as you'd expect from the peak speed.