I think that comparing to the USA (don't know about other countries) Russian sentences for violent crimes are rather mild. It's almost impossible to get life sentence for killing a person, and even for brutal crimes sentences often fall between 15 and 25 years. But "crimes against State/nation" are punished comparatively harshly. This situation is a part of juridical tradition.
Is it fair? It depends on your outlook. )

Also I really doubt that this American will have to go to jail for real.