You've inadvertently made an argument for deprecation, not ignoring rob's rule.

When building interfaces you are bound to make mistakes which end users will end up depending on (not just regarding optimization).

The correct lesson to learn from this is not "just dont make mistakes" but to try and minimize migration costs to prevent these mistakes from getting tightly locked in and try to detect these mistakes earlier on in the design process with more coordinated experimentation.

C++ seems pretty bad at both. It's not unusual, either - migration and upgrade paths are often the most neglected part of a product.