According to Mark, of all the weapons he designed, the Antimatter bomb is considered the best. Indirectly, just a couple of prototypes even stopped the world war.
If only the weapon wasn't banned by the upper echelons, who knows, for the future generations of the earth, Mark would have been called the father of anti-matter bombs.
However, it is also a truth that its creation is what caused his doom.
That doesn't mean Mark wasn't fascinated by designing it once again. They have so much potential. Not to mention the fact that he no longer has any superior to control his actions.
If he wants to create them, he could create them.
And the system gave him a shortcut to achieve it by providing anti-matter particles for free.
On any day, Mark would have chosen it without hesitation. But, as the system mentioned that he can only purchase one super advanced attribute, he wanted to make sure that he was making the right choice.