>>96577433
Your overall point is correct, but
>one quarter
It was much longer than that. But the data still goes in the direction you want. All this data comes from ICv2. There's issues with it, but it's the best we have so we run with it.
The first time pathfinder gets the #1 spot in in Q3 of 2010 (q3 is summer.) Where in Paizo tied with WoTC. Q3 for Pathfinder would have been the GM Guide, Advanced Player's Guide, the back half of the Kingmaker books and a handful of other books. Q3 for D&D was Monster Manual 3, Psionic Powers and Dark Sun. Plus, the other pathfinder core books are still pretty new. Speaking from anecdote - I knew plenty of people who did not buy Pathfinder until the GM Guide came out because they did not want to buy an "incomplete set."
Go into Q4 for Autumn and D&D is back on top. This corresponds with the launch of Essentials. D&D remains at #1 in Q1 (winter) of 2011. Paizo only really unseats them come Q2 (spring) of 2011. In that time, wotc put out Heroes of Shadow and the monster Vault. Compared to Paizo putting out Ultimate Magic, The Carrion Crown, a couple adventure modules and a few smaller books.
There's a pattern here. WotC is putting out a drip feed of books, while Paizo has their foot on the gas printing out all sorts of stuff. I'm not going to do quarter by quarter breakdowns.
But here's the wild thing. The last 4e book comes out in q2 2012. D&D remains in the top 5 sellers until spring 2014, and it pops back up in summer of 2014 in the #2 spot. I want to make sure this is understood - these were 4e sales when wotc was not publishing books and actively telling people that the new edition was coming. 4e was in the top 5 without trying.
But then the conversation stops there because fall of 2014 happens, D&D 5th edition comes out, and it runs rampant over the market. After that, all ICv2 information is paywalled and is harder to discuss.