You mean The durability of diamond head scales to Malgax and not his attack potency.
Because his punch produces this much energy.
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I also realized that this calculation is not 7-A it's actually
4.843 Kilotons (Small Town level+)
We used to have a calculation for 7-A Diamondhead it was this one
vsbattles.fandom.com
The problem with this one is that according to the merchandise cards and Ben 10 information diamond head and his species are made up of silicon which has weaker density instead of being made up of diamonds which this Calc assumes