What is the actual relevance of FTP in determining a riders Zone 2 heart rate on rolling terrain, and why do coaches insist on its importance when the traditional 7-zone model seems ill-suited for the nuances of varying gradients and road conditions? Does the conventional approach of using a percentage of maximum HR or pace to define Zone 2 not overlook the countless micro-adjustments required to maintain a consistent power output on undulating terrain? Is it not more practical to define Zone 2 as a specific range of power outputs rather than the more abstract concepts of HR or pace, and if so, what are the implications for pacing and interval training on rolling courses?