The general is the bulwark of the state. A bulwark is a wall or other defensive structure that is built to protect a castle, city, or other settlement from attack. In this context, Sun Tzu is saying that the general is the main defender of the state, and if the general is strong and capable, the state will be strong and able to defend itself. However, if the general is weak or ineffective, the state will be vulnerable and open to attack.
Now the CEO is the cornerstone of the company: if the cornerstone is strong and secure, the company will be successful; if the cornerstone is weak or flawed, the company will struggle.
The CEO is seen as the main defender and leader of the company, and their abilities and decisions have a major impact on the overall success and strength of the company. A strong and capable CEO can help the company defend itself against challenges and competition, while a weak or ineffective CEO may leave the company vulnerable to failure.