Dude have you ever physically measured one? I use a digital meter and believe me they point up, I am not trying to bullshit the OP or you.
The ONLY way you are going to make a driveshaft run vibration free is to have offsetting angles that equal 0* that makes it run parallel. The differential has to point down as it will move up as torque is applied to the rear springs, therefore the trans output must point up to offset the downward angle of the diffy. This is not difficult to understand there a dozens of online articles and videos that prove this out.
I agree that the OP has other issues that may be causing his vibration but if the shaft angles are not right is will shake.
I am out, again
