The F-16 and the F-18 were both sold as cheap alternatives to more expensive aircraft. We are very lucky that both of them were physically big enough to develop into the platforms those stripped down aircraft were intended to avoid. Both programs have been very successful.
Initially I think the F-16s were tactically considered more expendible even to the point of taking on the role of bait and decoys. They weren't considered as first class air dominance fighters. You can probably speak better for the Navy about the F/A-18 but I suspect that a similar mindset prevailed.
Obviously each proved superb for all the roles assigned and many not considered when designed. The Growler configuration comes to mind.
Frankly the F-16 can hold its own against 5th generation planes in terms of handling qualities. It only comes up short when the aerial battlefield suits the design philosophy of 5th generation fighters..