macOS isn't using my configured dummynet
By default, pf is not enabled on modern macOS. You'll need to enable it first by running this command:

sudo pfctl -E


If you prefer a graphical interface instead of the command line interfaces for dummynet and pf, you can use Apple's "Network Link Conditioner" instead. 

You can find it in the "Additional Tools for Xcode" package. If you have Xcode installed, it can be downloaded from within Xcode - otherwise you can download it directly from Apple's developer page (you do not actually need to have Xcode installed).

After downloading, you'll find it in the Hardware folder as a preference pane you can double click to install.

From the preference pane, you can enable/disable the link conditioner, choose which interface to have an effect on, and specify what you want to simulate (such as limited bandwidth, dropped packets, delays, etc).