A. How OD&D and the Early RPGs defined the Conversation.
My take is a bit different for this:
IMHO being first is
VERY powerful when it comes to RPG's
But, D&D also just got certain things right pretty much straight out of the gate from a game design perspective.
yes, OD&D did assume previous wargaming knowledge to fill in the gaps.
But it was first!
And no one had seen anything like it before.
TSR also upgraded the game fairly quickly to keep up with and stay ahead of the upstart competition.
OD&D
only had a 3 year edition life until Holmes basic and AD&D started rolling out. And they kept refining the B/X side of the game which covered for any of AD&D's foibles.
TSR upgraded and clarified things, while holding on to the things that it got right.
And once those elements were refined into what became B/X D&D starting with the blue box, none of D&D’s early “competition” had anything for them.
In addition to being first:
The 5 points that secured D&D's early dominance:
1: Easy PC creation: You could make a character and begin play in a matter of minutes. A selling point for new players.
2: Graspable Rules complexity: The first levels are not rules heavy. The mechanics were understandable. New players gradually got introduced to any additional complexity, easing the gateway for new players.
3: Easily grasped Default play mode: The Dungeon, an easy to understand and grasp mode of play. New players knew what they were gonna do right away. Explore a forgotten crypt, kill things and take their stuff.
4: Easily understood setting: Common Sword and sorcery fantasy tropes with lots of 'Tolkienesque" elements; Elves Dwarves, Halflings/Hobbits, Fighting evil Orcs, Trolls, monsters, etc... And Dragons! New players could easily imagine the kind of medieval fantasy land their PC's were adventuring in.
5: Straight-forward reward mechanism: The leveling mechanic is a great 'gratification' reward for killing things and taking their stuff. New players unambiguously knew how many XP they needed for the next level, and what to do to get it.
Yes you can point to the rules bloat of 2e and 3e, and how 4 or 5e fudge some of them and legitimately argue that some of those points got stretched more than a bit.
But by that time;
it didn't really matter as D&D had already cemented its market leader position. And the network effect of being the 800lb. Gorilla in the room smooths over any rough edges the system has.
Because as the market leader, D&D was/is
Good Enough that most players do not feel a compelling reason to go to a different fantasy RPG.
It takes a unique set of circumstances for
Being First + Good Enough to not be a winning advantage.
What is particularly interesting is that when you really think about things, virtually all of D&D's early competitors
failed miserably on more than one of these points.
IMHO how the early competition fell short:
Tekumel: Obtuse setting not newbie friendly.
Tunnels and Trolls: Group combat is a deal killer – Individual heroics in combat was gone. No other successful rpg has done combat the T&T way.
Chivalry and Sorcery: System complexity + Obscure default play mode = Ouch.
RuneQuest: Glorantha. I could just stop with that… But also character creation, and certain system elements. While a technically a more straight-forward system they dropped the ball on most of the other points.
In every case, D&D was delivering a more newbie accessible, better
overall game, than any of its early competitors.