If you're able to define a clear metric to objectively differentiate between "bullshit jobs" and "real productivity", you'll probably nab a Nobel in Economics.
If people could speak truth to power and bosses and didn't just suck anything up for the paycheck, we wouldn't need "a clear metric to objectively differentiate between bullshit jobs and real productivity".
Our intuitive understanding of bullshit jobs would be enough.
That's the easy part. The hard part is getting people to admit that the metric has been discovered already. Most problems with automation are organizational problems not technical ones.