But that is missing the main point of the network time checks. Even if computers were perfect at telling time you still need to check network time for security

But that is missing the main point of the network time checks. Even if computers were perfect at telling time you still need to check network time for security reasons, especially if local users can change the device time. There are crypto attacks that rely on changing the time, and checking that the time matches another somewhat reliable source helps make those attacks harder to pull off.