"What makes it even more complicated is that in a big org, knowing which tasks are important changes over time and with managers and manager's managers."

No, they don't. There is only one task in your job, to make your boss happy. Strangely, this is rarely achieved by good job performance but often by social skills or idiotic metrics. "How to manage your boss" is worth a read.

This is indeed called managing expectation.

There are various strategies one can "manage" their boss in return so that their expectation always remains at an optimal level, allowing them to easily satisfy their boss or even exceed all their expectations.

Everything can be manipulated, hacked, or "managed" as we professionally call it, as long as things continue to be operated by human. Even the largest corporations are susceptible and WILL succumb to this. Facebook and fake news are real evidences.

Their weaknesses just need to be identified so it can be exploited. External forces can even join together with more resources combined to execute their plans. It's not very difficult to identify weaknesses for many targets today, GREED and PROFIT.

Many corporations today only focus on their quarterly growth reports and would do absolutely anything to satisfy their investors. They don't even pay attention to their own customers, let alone those external forces.

Spontaneously two former superiors or mine come to my mind. Both unprofessional on an epic scale, they nearly tanked complete companies. Yet they succeeded in the only metric that counts: They made they superiors happy.

Your boss is the main person to make happy, but they are far from the only person. You also need to help your business partners, your manager's manager, and others.

My boss is the boss of 30 people and he can't really tell in detail who is doing good work and who not so much. The bar is higher than that.

Small suggestion: don't use the term 'boss'.

I have a manager, but I don't have a boss.

If your boss is happy, feel free to call them manager. When that manager becomes unhappy with you, you’d better be prepared to deal with a boss.

Companies that strive to improve their effectiveness can develop a methodology to apply this principle from top to bottom.

A good manager will identify the optimal point for each of his team members. This optimal point will serve as a target performance ceiling for managers to motivate and encourage their staffs to work toward to. If we try and push them over this point then we will begin trading output quality for needless productivity.

For someone at the top, it’s important to determine the optimal point for your organization’s current equilibrium state as well. The goal is to always operate within this state, but slowly and incrementally move the equilibrium point up over time as your organization develops and increases its capacity.

Depending on each industry, the degree to which this principle will affect organizations will vary. For example, it would be more decisive to those who produce creative content as their main output since the negative impacts can be very noticeable and highly detrimental, whereas a manufacturing business relying on human labor can be quite flexible in re-adjusting their capacity.