^^^ It's not a fixed percentage. It's not linear. The faster you go the greater the benefit. Even the marketing copy shows this.

If TOTAL time saved was the goal and aero benefits were linear and fixed then going 10km/h vs 40kph would mean that the slower rider saved more "time".

Since the real question is who benefits more then the real answer is a faster rider because aero effects become more pronounced at greater speeds.

Claiming a slower rider saves more time is just statistical manipulation. It flies in the face of common sense.