This number does NOT tell you it is harder for Asians to get in, or that their number is decreasing, for a couple of reasons
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it does not tell you the number of Asians, only the percent: if more people were admitted early, the numbers of Asians may actually have increased! We can’t tell from the info given
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it does not tell you the numbers of Asians who applied
There are all sorts of legit questions about how Harvard addresses diversity but you cannot draw this conclusion from the number you quote.