Control the opacity of dozens of layers via a dedicated “null” (no precomp, no one-by-one pick-whip)

In one comp I already use Null A to drive the size/scale of a group of elements. I also need a Null B to control the opacity of many layers (bars, logos, etc.) without:

• pre-composing those layers, or
• pick-whipping opacity one by one (sometimes 50+ links).
  Ideally, I could bulk-link multiple layers’ opacity to a single controller (null/effect controller), with a quick way to (re)connect/disconnect layers, and have it coexist with the existing parenting for Scale (a kind of “multi-control”: parenting for Scale + global controller for Opacity).
  An explanatory video is attached to the ticket to show the current setup and the desired outcome.

video explanatory and desire result