High/Low fighter mix consisting of a smaller number of very expensive air superiority/supremacy fighters complemented by a larger number of less expensive fighters (usually attack optimized). It gives you that sharp performance edge if you go up against a high-end opponent, but still allows you larger numbers of switch-hitters for various circumstances such a low-tech foe with a crap-load of airframes.

It's a common strategy, this is what we did with the F15/16 and F14/18, and more or less what the russians have with the mig29 & flanker.

Other folks do it too.