I'll agree with that. It is after all why the PHB is the best selling book for 5E, because it is truly nearly 100% player focused. I think it is safe to say however that many players purchase Xanathar's who never intend to DM. Checking it now, it is still the best-selling non-core book (not including the ones to-be-released, and Tasha's), and even has more reviews it than even the Starter's Kit (14,000 vs. 12,000).
Tasha's is selling even more right now, and has 10,000 reviews, which is more than any non-core rulebook. So I assume the amount of player material puts these books a tier above in popularity compared to adventures and settings.