Maybe productivity should not be regarded isolated from other metrics and/or certain style-considerations.
It seems to make sense:
N * (debt factor) = debt
10N * (debt factor) = 10 * debt
developers have personalities with differing values. That super productive developer may just not value the flexibility of the code due to his personality coupled with that developers personal experience.
That developer will absolutely shine in some environments and be abysmal in others since there are absolutely environments where flexibility isn't an overriding concern.
As you get more experience you learn to be more explicit about your decisions, but you'll still have your preferences and your defaults and it takes a certain threshold for you to move away from said preferences and defaults.