Rat skinner, I'd largely agree with that. The system is going to influence how a world looks to some degree. DnD is idiosyncratic and frankly inflexible enough that any DnD world is going to share a fair bit of similarities.
If nothing else, the class system imposes a number of constraints.
But, that's a fair distance from saying that DnD is meant to be a world building game.
Which is why I finished with:
On the general point, however, I totally agree.
Most D&D settings pay attention to at least some aspect of D&D. Especially some of the aspects of D&D which take place in areas the PCs are unlikely to use (for me Planescape games are basically about Sigil and the Factions - and those don't map to alignment neatly). Bits might take inspiration from D&D but even Eberron doesn't entirely use the D&D rules (which for 3e would end up with something like a
Tippyverse or the
Tome of Awesome).
I'm not saying that I think the rules are a good starting place for world design, but let's take a look at the quote to which I was responding:
The only D&D game world built on D&D assumptions is Eberron. None of the others are. There's how many D&D settings just from TSR/WOTC? Ten, twenty? Only one of them gave the slightest toss about the mechanics of the game that was being used. It's always been world first, mechanics second. And the mechanics are pretty obviously meant for PC's only.
I think that is overstating the rules-neutrality or system agnosticism of D&D worlds quite a bit. FREX: 3e, IIRC, pretty explicitly had NPC classes which were intended to be counterparts to the PC classes. I suggest that the mechanics for that edition, at least, are
not intended solely for PC use. At least one 2e source (although I cannot recall which one, possibly the DMG) mentioned worlds that were conceived with silliness akin Tippyverse or the like (including Djinn-powered steam engines, IIRC.) Which does not imply that I think that the rules
should be a starting place for designing a world.
Sure anything I build with Lego is going to share a certain blockiness. But that doesn't mean that I'm constrained to only building certain things.
If the mechanics of DnD come first in world building the every DnD world would have to be pretty much the same. But, once you step back and build the world first and then apply the mechanics you can do pretty much anything.
I would contend that this, as well, is overstating the reality. For example, building a ball with legos is a bit of task (to extend your metaphor a little.) While there is, indeed, a wide realm of possibility under the D&D umbrella, it is far from limitless. Running games in other freeform systems like Fate has, for me, illustrated by contrast how the D&D rules subtly but profoundly influence many aspects of its worlds.*
The mechanics of D&D don't have to come
first to have such an influence on the setting, they simply have to be present in the mind of the designer
throughout the process. I have a difficult time believing that setting authors somehow divest themselves of game knowledge during the conceptualization phase, only to re-introduce it during some final system-readiness audit. To return to your metaphor, given a bunch of LEGOs and setting about the task of building something cool to play with...one will not likely even attempt to build a playground ball. Rather, knowing the nature of the tools at hand (LEGOs) one will set about building something that is cool to play with that has or utilizes that certain blockiness from the outset.
*Which is not to say that those other systems are free from analagous influences or limits on their settings, either.