Other governments use drones to bomb people in various countries with impunity.
If a private citizen does any of this sort of murder of their own accord, they go to jail. The difference between government and private citizens is that the former can exempt itself from the consequences of these heinous acts. That is what is meant by the term “monopoly on violence.” [1]
Also, your opinion on what is murder is arbitrary. All your criticism really is is, "I don't like the definition currently used". That doesn't contain any reason why it should be modified or how or describe any principle.
A monopoly on something doesn’t mean exclusive, 100% godlike control of it. It just means the legitimate provisioning of that thing falls under the authority of one entity. Copyright is a government granted monopoly on the right to copy a creative work but that doesn’t make it impossible for others to make copies, it just makes it illegal.
A state, and words and concepts, only exist insofar as people believe in them. You're only saying "murder is [defined]", not anything about governments. If you pretend you are making a statement about government or politics, it suggests that somehow a different system could achieve a better and different state. Everyone defining legal killing for themselves is not better or worse, it's a contradiction in terms - an absurdity.