When tasks and skills are a good fit and everything’s well-prepared, then people are fast.
If you manage to get your project to always be a perfect match for your current skills, you can be much faster.
But has to do things for which they aren’t a perfect match – either too deep in the topic (⇒ bored) or not deep enough (⇒ out of their league). And in productivity numbers, those will look back.
And if you managed to organize the project such that all tasks are always a perfect fit to the people you have, that project could see awesome productivity.
Everyone always having a fun challenge that they succeed at and learn from.