This usually isn't true at scale though. The chip manufacturers do a ton of validation and qualification to set the operating parameters (voltage, etc).

You can undervolt (or overclock) one specific chip, individuals have been doing this at home for basically ever, but there's (almost) always a system-specific validation process you then do to make sure the system is stable for a specific workload with the new parameters.

And these parameters differ between batches of chips, or even between chips within a batch.

It's also significantly harder to drastically reduce the temperature of the chips inside of a single server, given the machine density of a typical data center.