Also, as I mentioned, they were releasing BECMI, Dungeon (I believe, not sure when it ramped up), and Dragon magazine. That all counts as content, you cant just separate out 1e and say they were slower.They are not. From 1977 to 1983 TSR put out the PHB, DMG, MM, Deities and Demigods, Fiend Folio and MMII. 6 hardcover rulebooks. From 2014 to 2020, WotC put out the PHB, DMG, MM, Volo's, Tasha's, Mordenkainen's and Xanathar's. One additional book. And Starting in 1984 TSR started producing much more content.
Settings and adventures are NOT rulebooks. At least not the way 5e makes them.