One of the things I learned in business school was that being first entrant into a market is the single biggest factor correlated to success in that market. More than 60% of market leaders across all industries were the first entrants (or successors in interest).
That advantage isn’t unassailable, clearly, but it’s huge. The #1s still need to work hard and adapt to maintain their power or they’ll be surpassed by competitors.
Yup RPGs still to niche fir a competitor to emerge. Unless D&D defeats itself.
I suspect a Sci fi rpg might one day beat D&D if I had to guess a genre.