I'm not a great expert on assembly lines, to be honest. But two things:
- From theoretical considerations (less important): you can be better not just by improving average speed, but also by reducing variance (ie being more reliable) and improving quality.
- A practical consideration (more important): from what I recall, even people on assembly lines are often paid piece rates. Ie they are paid more or less proportional to their output. Assuming companies aren't complete idiots, we can assume that they have a good reason for rewarding individuals for higher output? That seems to be in at least mild contradiction to "The assembly line is as good as the worst/slowest person on it, [...]"
- From theoretical considerations (less important): you can be better not just by improving average speed, but also by reducing variance (ie being more reliable) and improving quality.
- A practical consideration (more important): from what I recall, even people on assembly lines are often paid piece rates. Ie they are paid more or less proportional to their output. Assuming companies aren't complete idiots, we can assume that they have a good reason for rewarding individuals for higher output? That seems to be in at least mild contradiction to "The assembly line is as good as the worst/slowest person on it, [...]"