The problem here, I think, is that the founding fathers didn't foresee a situation where a country goes to war, without formally declaring such. I don't think the military operations we conduct now were ever contemplated as part of their 18th century understanding of the world.
That's why we eventually ended up with the War Powers Act.
More broadly, wars in the 18th century tooks months to warm up. You had to call the regiments together, or raise the citizens militias. This takes time. And even if the war was against a next door neighbor you would still have to assemble everyone near the border, get all the equipment brought in, and the officers assigned. Shit took weeks to months.
God help you if the war needs to happen in a country that is not next door to you. Now you have to start thinking about sailing ships.
In this context, giving the legislature war deciding power makes sense. Even if you want to attack someone, they will have weeks to months to think about it. And its not like you can hide what you are doing from the neighboring country, so even the operational security excuse doesn't really apply.
Now though, a war can get started within hours. Or the opportunity to strike a decisive blow right at the start by surprise (as happened here) is possible but would require a hair triggers notice. Suddenly its not quite so clear cut that Congress needs to spend weeks dithering about whether or not war is needed.
This also doesn't factor in the fact that there is no such thing as a "loyal opposition" in America anymore. Whoever is in charge will be opposed lock step by whoever is not, for any reason or pretext. Which would hamstring the war deciding capability of the nation. Which would be a disaster. If American enemies assume the USA is incapable of fucking their shit up because the decision on fucking them up is dying in committee or getting filibustered, they aren't going to take anything we say seriously.
