I don't have good data for this, but what I hear and see suggests that D&D isn't achieving its awesome growth on the backs of hardcore invested gamers. Just as 50% of all 5E players are new to the hobby with 5E, I think a lot of purchases are point-of-sale type impulse/interest buys for new and casual players. I suspect that it is a fairly narrow segment (more invested, less casual) that would find itself on D&D Beyond purchasing Planescape vs the far larger group that would purchase the book via a store or online retailer.
D&D is big enough that it really matters what is on a shelf and how the products appeal to the person that happens to walk or scroll by. What can happen is that the shelf can become confusing and overwhelming.
Something I like to do when I travel around the US is look at the gaming shelf in a store (whether big box or local gaming store). I pretend I'm a new gamer. Can I find the products I should buy? Can I easily find this edition and the latest books vs traps? For much of 5E, it was pretty clear. The Starter Set and Essentials were equally great on-ramps, the core books were pretty clear, the adventures were all equally good/bad for new DMs. Now, you might find five Starter Sets (do I start with Rick and Morty?) and you might find an old Mordenkainen's or Volo's vs a Multiverse set. And next year you might get confused between 2024 and 2014. That's where the glut really has an impact, rather than the more narrow issue of releasing 8 books in a year. The shelf glut is a big problem for walk-ups. The 8-in-a-year is a bigger impact for the hardcore gamer (which also can impact the shelf glut).