Fine, I read it, happy? Not seeing any of your supposed "proof" though. You showed a few links of base Natsu kicking his ass, and then said Zeref treated the fight like a game. Can't say I'm overly convinced by your argument.
First of all , he wasn't "kicking his ass". Second of all , there wasn't use of any magic in the fight. Zeref is known for being an exceptionally strong wizard , not puncher. And third , when Zeref actually used a proper spell , Natsu was completely overwhelmed and was forced to go Dragon Force because of one casual spell. Dragon Force is not the same as Base Natsu , this is the form in which he wrecked Animus , who was powered with Dragon Cry , the strength of multiple dragons. And Zeref is above him. This was not even using all the other hax spells I mentioned he is capable of using , just one immoblizing spell.
Law was capable of oneshotting the Tenrou Dragon.
He can stop time and oneshot people.
He enchanted Irene into a human from a dragon in an instant.
Irene required so much time to take Fairy Heart , he did it in seconds.
He used spatial magic to close the rift gate from the guild itself.
Not to mention his demon , Larcade , would floor CS , since he was capable of flooring Gildarts and Laxus too. Zeref isn't even needed.
The fact that some actually think Zeref would lose to CS is kekworthy , when they don't even check the context of the fight. Larcade would floor CS , let alone Zeref.