If Deidara didn't have such a huge Aerial advantage, then I'd give it to Hiashi. But like DK said, Deidara will overpower Hiashi. Not low difficulty though. Somewhere along the lines of medium difficulty, because Deidara will still have to deal with Hiashi being able to deflect things with Rotation and avoiding Air Palms until Hiashi is tired out.
Rotation could in theory block an explosion but it won't reflect it back at deidara or anything.
Dei takes this low diff. Zex doesn't even need to come argue this i got this one lol
If Deidara didn't have such a huge Aerial advantage, then I'd give it to Hiashi. But like DK said, Deidara will overpower Hiashi. Not low difficulty though. Somewhere along the lines of medium difficulty, because Deidara will still have to deal with Hiashi being able to deflect things with Rotation and avoiding Air Palms until Hiashi is tired out.
I also have doubts about C4's nano-bombs being able to bypass a chakra layer that Hiash could enforce around his entire body.

You must be registered for see images
Unless you're insinuating that neji is in a vacuum when he does rotation, air (and by extension the nano bombs) can still enter the system.
That's not how this works. Neji releases this chakra to push things away from his body, which is how it stops the kunai's, etc. Neji simply needs to keep releasing chakra from his body at bursts until he's left the field of bombs. And that's assuming he didn't destroy the C4 with Air Palm before its 'popped'.
C4 won't be effective against Hiashi, or any Hyuuga for that matter:
You must be registered for see images
I also have doubts about C4's nano-bombs being able to bypass a chakra layer that Hiash could enforce around his entire body.