Yes. As another poster wrote, other P3 trials have had to be large in order to get enough safety data and to try to get N high enough that even a small effect would generate a statistically significant p number. In the case of 2-73, if 509 is not enough to generate a good sized effect with a very low p number then it doesn't deserve approval. And there are collectively enough patients being dosed with 2-73 across several indications to provide strong safety data.
Read your own cited source ("300 to 3000"). The nature of the indication being treated is what dictates 'acceptable' phase 3 size. AD is on the very high end. Biotech investors know this stuff. This is not fantasyland.
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