Long term stock price is the measure of long term performance.
Let us say a new President of the company is hired in 2024.
As you say we have no idea whether they will last just six months or twenty years.
However, the long term compensation simply says that there will be deferred payments (details in employment contract) that will be based on the stock price in 2034.
Obviously those payments cannot be made until 2034.
That would motivate the President to think long term.
In addition to long term thinking, a good strategy and the CEO's skills, character, and dedication to task matter, as do that of the other members of his team, and the quality of the board's supervision and support.
In addition, market conditions, consumer preferences, and regulatory environment have their effects, and the performance of Boeing's divisions depend on company culture and the quality of people deep in the ranks. The many elements and the costs and risks inherent in airline design and manufacturing make it a "sporty game."