I want to restore my iPhone battery performance to full capacity

It's great that you've recalculated the battery capacity and shared your findings. Battery capacity and health can indeed vary based on multiple factors, including usage, temperature, and the specific chemistry of the battery cells. Your calculations seem accurate, and the capacity loss you've noted is significant, especially for a relatively new

MacBook Pro with only a few cycles.

Apple's in-house diagnostics may provide a different result because they can use proprietary algorithms and criteria for determining battery health. While it's essential to consider their assessment, individual users can monitor their battery health through System Report or third-party apps for a more detailed view of their battery's status.

If you find that your MacBook Pro's battery capacity continues to degrade rapidly or falls below a level that's acceptable for your needs, it's a good idea to reach out to Apple's support for further assistance. Under certain circumstances, Apple might offer battery replacements, especially if the battery issues are deemed unusual or excessive.

Additionally, for MacBook users, it's always a good practice to take care of your battery by avoiding extreme temperature environments, not leaving it plugged in continuously, and periodically running full charge-discharge cycles to help maintain battery health. You can also use tools like this calculator to help with your battery capacity calculations.

Battery capacity that has decreased over time cannot be regained.

The only way to get back to a 100% capacity is to replace the battery with a new one.