Well I'll get straight to the point, looking at it from deidara's point of view being that is my argument.
Deidara has something Minato doesn't range. Sure, Minato can throw a Hirashin kunai, but how far? Deidara specializes at long range battles, namely from high in the sky. And if even one of his attacks hits, it's going to be pretty devastating. Though, if Minato can use that Space Time Barrier he used to teleport the Kyuubi's attack to teleport one of Deidara's bigger explosions, he might get a bit of an edge. Deidara could theoretically win a ground battle as well, give that he stays a far enough distance away. He has homing bombs that move on their own, as well as microscopic bombs. He can manage a battle from half a mile away.
Its possible that Minato could try to catch him in the air through some ingenious Kunai throwing chain combo but i don't think it is a sure thing being that their's factors like gravity to consider..also at a given height it may take some time for minato to get there.
What about C4? We know C4 is microscopic and a cloud. Clouds tend to envelope. I don't think he'll be able to protect himself from all of it. He might not even see it. As I recall, Sasuke didn't until he used his Sharingan. The only hope Minato has of avoiding C4 is if the Jikukan Barrier technique is able to protect him from it by chance. And even then, it's unlikely it'll protect him from all of them.
I see a very possible counter here for Minato's Fighting style and FTG.