Hello,
While AU is the MacOS native plugin format, Steinberg and many other daw developers do not support AU. VST as you know is Steinberg’s format and works fine in MacOS. I wouldn’t phrase it as “less efficient” just different. There are some situations where the AU format is preferable and others where it’s not, but those increments are swamped by the fact that VST works fine on MacOS.
Using Cubase or Nuendo on Mac or pc involves moving the elicencer dongle, no cost.
Hugh