How to prevent heavy rainwater from jumping the gutter?
This is a common mistake, which will lead to premature roof wear.  What the installer should have done, was to install an A to B transition elbow, and continued down the roof with a section of down spout. Then used an A elbow to have the water dump directly into the lower gutter.

It should end up similar to this



Allowing the high volume of water to flow over the roof, will damage the shingles and cause them to wear prematurely.  Even if you turn the spout adjacent to the slope, it will still cause damage to the roofing. Spreading the flow over the roof in this way, will not alleviate the damage that is caused.  In either case, you're allowing all the water shed from the upper roof, to flow over a small section of the lower roof. It's a terrible idea, and should be avoided.

I'm not sure exactly when builders decided to try and save the $10, by not installing the downspout along the roof. But it makes me so sick every time I see it, I just want to climb up there and fix it myself.