I mean:
-Zeldris himself already stated that it doesn't matter how strong his opponent is, he never underestimates them and always goes all out.
- Zeldris knew that Merlin was the witch who tricked both Gods. Not only that but he had her in extremely high consideration (even Merlin said to him that he was overestimating her).
Based on Zel's character and opinion on Merlin, it makes no sense that he had the DK's magic deactivated. Why would he do that in the first place?
IMO, Nakaba didn't know very well at that time what the DK's magic could be. At first, it was supposed to be a sealing magic judging by how Drole couldn't use his magic after being kicked by Zeldris. Let's look at the feats before it was revealed to be Inversion:
- In chapter 246&247 Mel overpowered the DK's magic with an attack that even Estarossa (60.000) could resist better.
- In chapter 250&251, Ludoshel casually bypasses the magic in a nerfed human vessel.
Now, let's look at the feats after it was revealed to be Inversion:
- Absorbs without any problems Ludo's Gold Shining, technique that we can assume is above the greeting he used against him before.
- Absorbs Merlin's magic without any kind of difficulty.
- Absorbs King's attack (who should be around 200.000-300.000) without any problems.
It's pretty clear which one has the most impressive feats. Possible explanations to this:
A. Zel had the DK's magic deactivated and that's why he got hurt by Ludo's attack. Mel would need to be above King in magic if we assume that what he used was magic (at least that was the implication). This overall makes little to no sense.
B. The DK's magic was supposed to be something different and Nakaba changed his mind. Therefore all the feats done before it don't count for anything.
C. Zeldris and the DK's borrowed magic got exponentially stronger because plot reasons.
