That is an easy question to answer.
Look at it like this. To people, A and B, do something.
Person A takes 100 seconds to accomplish the first task and person B takes 1 second to accomplish the task.
Person B is 100 times faster. (100 vs. 1)
Now, we make them perform a second task. The second task takes them both 50 seconds.
They are equal.
Now we make them do both tasks.
Person a takes 150 seconds (100 + 50) and person B takes 51 seconds (1 + 50).
Now person B is only 3 times faster instead of 100 times faster.
That is what you have. Sure there is a huge difference in the overhead of the first task. But the minute you start adding more tasks that are equal, it soon begins to average out.
Look at it like this. To people, A and B, do something.
Person A takes 100 seconds to accomplish the first task and person B takes 1 second to accomplish the task.
Person B is 100 times faster. (100 vs. 1)
Now, we make them perform a second task. The second task takes them both 50 seconds.
They are equal.
Now we make them do both tasks.
Person a takes 150 seconds (100 + 50) and person B takes 51 seconds (1 + 50).
Now person B is only 3 times faster instead of 100 times faster.
That is what you have. Sure there is a huge difference in the overhead of the first task. But the minute you start adding more tasks that are equal, it soon begins to average out.