Well by the nature of this concept of a "mandate from heaven", he kind of have to take this position. If the founder of the Ming dynasty claims he now has the legitimate devine right to rule China by taking this mandate from the preceding Yuan dynasty, then by definition the Yuan dynasty must have been at one point legitimate. After all, if they were never legitimate, and then you took the mandate to rule from them, that would mean your own mandate is also illegitimate.

Therefore the official stance of EVERY major Chinese dynasty has to be that the previous dynasty gained the mandate of heaven legitimately, but then lost said mandate due to poor rule, thereby allowing the new dynasty to claim the mandate and begin the cycle anew.

Interesting side note about the mandate is that there was once a physical symbol of it in the form of a massive jade seal made by the first emperor of China around 220 BCE, which survived multiple pronged periods of interdynastic chaos, until eventually the Heirloom Seal of the Realm was finally lost to history somewhere around the Song to Yuan dynasties. Zhu's forces looked very hard for the seal as they took over the country from the retreating Mongol five, but came up empty.