It's more about being able to deliver it when many cars are charging. Charging speeds go down considerably. I typically don't get the maximum possible speed and often am far off and sometimes that depends on the number of cars charging.

Your actual limitation when the site is full is usually the utility transformer. Tesla have been installing many 8 stall and even 12 stall sites with 750kVA pad transformers.

If they had a Tesla Megapack as a buffer for example the transformer wouldn’t be the bottleneck as the output is greater from the Megapack.