Osama was more like Gorbachev's rival. Then he had the betrayal arc with Bush. Obama taking him out was the writer having the new villain kill the old one to show how strong they are.
it's actually kind of like the serial number, he started with Oaama and Obama but the Oaama didnt work out, nor the next few, so it wasnt until he got to the letter S that he got the correct proportions for the recipe