This is true, but like in the US these laws are not evenly applied. Russia also has a history of giving more severe sentences to foreigners, perhaps as a negotiating tactic.
Once again, I don't disagree with you, but laws are not just when the sentences are different depending on who you are. If you argue that the law applies equally to Russians as to foreigners in Russia, then the sentences should also be equal.
And again I’ll say: foreigners need to follow the laws regardless as to how harsh they are treated (relative to local citizens or not) for breaking them.