We have strayed from the original question a bit (onto landing little trainers in a X-wind????)

One answer I have offered is that it keeps the tailplane tips further off the ground on landing without having to raise the mounting position.

Sweep back has to do with Mach number, dihedral does not. Main wing dihedral (and sweep) affects lateral stability, but tail dihedral has a negligible effect.

Lnewqban.
That hairy scary video does not show how it ought to be done, though the ones of the new Boeing Dreamliner are good, the first showing how the U/C can take landing still with drift, and on the second touchdown is on the into-wind wheel.