This is true, but it doesn't solve the problem. If you give Docker half of your overall resources, it's just going to take Docker twice as long (most likely longer) to finish running the test suite or whatever you're doing in Docker. The crux of the problem is that Docker for Mac has pathological cases, probably involving host-mounted volumes that are big or overlaid or something else that we were doing; the containers can be near idle and Docker for Mac consumes 70-100% of its CPU budget (presumably doing volume/filesystem things).

Note that a little Googling reveals that this is a pretty common problem.