Of course there is truth in what you describe. But an increase in national GDP is possible in some cases, especially if the country obtains arms purchase contracts from other countries. The most felt negative impact is for countries involved in war, while other countries actually benefit from the war.
Oil is a very important resource in the modern era, not only during times of conflict. Because all transportation uses oil, and we can calculate how many transportation there are currently in the world. However, war is a factor in fluctuations in world oil prices.
Weapons factories also need oil when making any production for war needs and this is clearly felt by all countries that have weapons factories so that petroleum is not only used for transportation. Apart from that, electric transportation manufacturers also need more oil as their energy source because without oil, they cannot produce electric transportation equipment such as motorbikes and cars. Meanwhile, in the war sector, oil is also used for jet aircraft and warships, so the impact on the price of oil itself also has very unstable fluctuations in the market.