I don’t think that the literature allows you to draw that conclusion. In fact, quite the opposite, i.e., the largest increases in mitochondrial respiratory capacity have been found in studies with the most intense training programs.
Because (seriously!) there is no such thing as “zone 2” (or zone 4, etc.). Such distinctions, while sometimes useful, are almost completely arbitrary. In point of fact, exercise responses and adaptations reside on a continuum, and you have to go well up the intensity spectrum before things might start to change significantly. Even then, since recovery is essentially a 100% aerobically-fueled process, you will actually elicit the same adaptations by performing really high intensity, short duration intervals if the rest periods are kept short enough.