The calculations within each unit may be, true, but routing and data transfer is probably the biggest limiting factor on a modern chip. It should be clear that

The calculations within each unit may be, true, but routing and data transfer is probably the biggest limiting factor on a modern chip. It should be clear that placing 16x units of non-trivial size means that the average will likely be further away from the data source than a single unit, and transmitting data over distances can have greater-than-linear increasing costs (not just resistance/capacitance losses, but to hit timing targets you need faster switching, which means higher voltages etc.)