F-5 effective aggressor?

With the the world supply of Mig-21’s & Mig-23’s quickly disappearing. Why would the USN invest in more F-5’s from Switzerland? It’s current fleet will last to 2010-2015. Most 4th generations fighter will start to be replace over the next 10-15 years. Let alone the generation before that! IMHO I have my doubt the current Hornet’s from CVWR-20 will be up to the task in the next 10-15 year time scale. (i.e. with Rafales, Typhoons, Su-30’s, Gripens, LCA, J-10’s etc.)