I think something should be said about torsional rigidity in the crank. A V6 would have a shorter crank and therefore would have the potential to be stronger.

I disagree that most v6s are 60 degree. Nissan, Alfa and Chrysler made 60 degrees, but almost everyone else including Mercedes are 90 degree.

The problem with the 60 degree is that the bore is limitted by the block angle. You can only go so big until the banks of cylinders start getting in the way of each other. You have cooling issues and if you like big flat combustion chambers (lots of valves) there are limits.

I think the inlines are easier and cheaper to manufacture. Fewer number of cams and a simpler valve train. The 60 degree v6 is smoother than an inline IMHO.