There's a reason why queues are more performant than threads. See node.js and nginx for real-world examples.
The OS is dumb and does not understand the nature of load. If we applied your logic, everyone would still run Apache instead of nginx.
Your user-interfaces 101 fails flat on its face when you have hundreds of short-lived jobs that need to happen. Each one is insignificant on it's own, but if you overload the server will all of them at the same time just can starve system's RAM (forcing it to swap) or increase disk seeks by order of magnitude if short-lived jobs are asking for different data that is all over the place.
The OS is dumb and does not understand the nature of load. If we applied your logic, everyone would still run Apache instead of nginx.
Your user-interfaces 101 fails flat on its face when you have hundreds of short-lived jobs that need to happen. Each one is insignificant on it's own, but if you overload the server will all of them at the same time just can starve system's RAM (forcing it to swap) or increase disk seeks by order of magnitude if short-lived jobs are asking for different data that is all over the place.
The only true answer here is: it depends.