Here's the thing, ads and all, the first issue of
Dragon Magazine was 30-odd pages. Including adds, silly comics, not D&D content and illustrations. If you include the five articles on the WotC website released in February and a couple of the previews, it's also about as much pages.
So we're seeing exactly the same amount of content for 5e as we saw for 1st Edition AD&D. And, if you look back at what was in Dragon in those days, the content is a heck of a lot better.
Even including just Tyranny of Dragons and the Adventurer's League adventures (and not the pre-launch 5e adventures), we've seen a comparable about of adventure content, the equivalent of six 32-page adventures. And we're going to see even more in the next month, between
Princes of the Apocalypse and the free content PDF.
It's very likely 5e will blow 1e out of the water in terms of content per year. And that's before you consider that we saw all three Core rulebooks in the same year rather than once a year.
And the second WotC releases an OGL, there'll be a flood of content that will likely dwarf the content of 1e and even likely 2e. That's excluding all the stuff
fans are already putting out.
5e only has a slow release schedule when you compare it to 3e and 4e. Which is like saying the Appalachians are small when looking at the Rockies.
--edit--
I thought I'd take a closer look at the numbers.
As a comparison, take at look at what TSR released for adventures during 1978*, the middle year of the AD&D rollout:
B1- In Search of the Unknown
D1 - Descent into the Depths of the Earth
D2 - Shrine of the Kuo-Toa
D3 - Vault of the Drow
G1 - Steading of the Hill Giant Chief
G2 - The Glacial Rift of the Frost Giant Jarl
G3 - Hall of the Fire Giant King
S1 - Tomb of Horrors
(*1978 was the prolific year. Content in both 1977 and 1979 was much more sparse)
Ostensibly a nice mix. It was a year of classics. But, when you look closer, it's really a 1-3 adventure and then an 8-15 superadventure. Only 128-pages of adventure (including the art booklet from
Tomb of Horrors). The Tyranny of Dragons adventures contain more adventures and 64-pages of extra content. And once
Princes of the Apocalypse drops, there'll be another 120-odd-pages of content above and beyond that.
Quite frankly, after just six months, 5e is kicking 1e's ass in terms of pages. After a year, it'll be no contest.