If we're not fighting yet, Mm having a deadlier weapon makes the cost of attacking me higher for my enemy, discouraging him. If we are already fighting, having a deadlier weapon will mean I kill more of them than they kill of us.

My enemy having a deadlier weapon makes it less costly to attack me, and makes them kill more of us.

So yes, having a deadlier weapon makes us more safe. The alternative to nobody having it is preferable, but that would require an enemy who will cooperate with me, which is a contradiction in terms.