Both matter. Execution doesn't progress without the capacity to think well. Learning to think well doesn't progress without littering and clearing the mind of thousands of ideas. It's a careful balance of maintaining a signal in the noise.
It's more humorous to consider maths and programs as ideas. And when I say humorous, I mean that very seriously.
But, going with that: Conversely, a better execution may be more difficult to implement successfully.
My original point was that the G-GP's statement was self-evident to the point of meaninglessness. You could flip the bits the other way and say something equally as meaning-ful(less).
Both idea and execution have some level of importance, but holding one constant while improving the other does nothing to discriminate between the relative value of either.