Board Thread:Speculation House/@comment-30541831-20190401034421/@comment-26018514-20190401040153

It means Ozpin's "stockpile" of powers are finite, not that the powers themselves aren't infinite.

Salem's powers are the only remaining full magic from Humanity one, they are also the only powers tied to an immortal body, so it may be possible Oz loses some magic through each iteration, or that the ability to maintain full magic functionality went into the maidens, starting his decline, you'll note nothing has been said about the Branwen powers being inheritable.