Yes, they are both weapons and have destructive potential; on that there is no argument. However, the destructive power of a nuke over a gun is so massive that there is no relative comparison and I do not see the point of your argument. Let me put it this way.
Let us be over generous and say that a gunman at a soft target (schools and other no weapon zones) kills 100 people, hell let us go overboard and say 500. That sucks, hard!
Kim Jong Un, the crazy fuck, decides he wants to nuke Tokyo (population 9.2 million). Millions of people die, many more in the surrounding areas die horrible deaths due to the radiation and the land can not be safely inhabited for years.
Again, yes both are weapons and both are destructive but the use of either yields completely different results. Your not comparing apples to oranges here.