No, economics is much much more complicated than 59+111. Elementary students in China (high school in the US) can all easily solve 59+111 with a definitive, non-disputable answer. However, even top economists often cannot accurately predict economic effect from markers or market effect from decisions/event properly. As a matter of fact, 2 top economists can look at the same data and interpret them to indicate opposite things from each other. A lil' more complicated than arithmetic.
That little ending paragraph you posted is what you think will happen based on your highly limited experience analyzing a very limited number of factors in an entire field of possibilities. Do not try to pretend that Keynes said that because you clearly cannot find anywhere in which Keynes said that a trade war will benefit the country running a deficit. If you're trying to interpret what he said to somehow mean that, then say so, because that is very very different from him directly saying it.
C'mon. many math field more advanced than the normal primary school math, but it doesn't means that they don't have to obey the basic math rules, like 1+1=2.
So, doesn't matter what economical theory anyone dream, if it not satisfy the basic rules then it is FALSE.
The economy best part is a social science. many of its rules are just simple low level, limitedly usable rules, many cases only for same specific political reason.
Example the Neolib theory consider as the most important the equity and keeping stable the whealty.
You can use many rules in this framework.
Keynes considering the well being of the population as most important, and organise/use the rules in accordace with it.
See the demand/supply curves, and price elasticity.
If you use it for the job market, then you can quickly relaise that every other market will be deinfed by this . The neolib consdier the job market by the same way as say oil or gain market, Keynes saying that it is the most important market, and the main job of the goverment(country, society) is to keep it as seller's market.
And it connected to the long term prosperity of the country.
The only thing that is in limited supply is the worlforce only.
Every country success is dependent on its capability to use most effectivly its workforce.The GDP difference between China and US is due to this. It is possible only if the job market is allways tight, and the businesses has to found new ways to do more with less.