Phil Maffetone’s philosophy prioritises health over performance, and this is admirable for the long term.
However, training to perform well in a Marathon/Ultra etc, can never really be considered to be healthy. Optimal training means running large frequent volumes with accumulated fatigue, over many years. In such training, the Taper period is crucial, prior to the race. Would there not be an expectation that fitness would decline, as shown by a MAF test, during this long build up of accumulated fatigue?