No. When implemented correctly, with async/await you run one thread per CPU core or thereabouts and that thread runs continuously, picking up async tasks when it can, whereas using threads you'll have say 100 threads and each core is picking up threads when it can. And switching threads on a CPU core is a much heavier operation than switching tasks on a thread (you have to switch the whole 4k stack, rather than just whatever's in the task).

It's very possible to stuff it up, to have a conventional thread pool end up competing with your async-handling threads, you can get priority inversions where the OS thread scheduling competes with the task scheduling, and plenty of other pitfalls. But done right async/await should be significantly faster than threading.