Depending on how much input Kirby had on the cast. Considering the FF cast was EXACTLY the same as Sea Devils and Rip Hunter, and a set of parents away from Cave Carson, the stretch of a "four elements" theme seems weak. Me, I'm going with the huge blinking neon lights of the first two and the solid neon of Cave Carson.
About the only advantage the Challs had in being THE FF inspiration was the variety of adventures where the other three teams were limited in adventure scope. Also, keep in mind the FF had underground, time travel, and undersea fights in their first five issues. I remain far from convinced.