It’s a pool with a lot of constraints on it, many of which are artificial.
Based on? There aren't even many good technical writers, which is a lot easier than writing fiction.
It really boils down to a few gatekeepers (mostly old white guys) giving the screenwriting jobs to the same idiots over and over again. For example, the guys who wrote Morbius have never written a successful film that made money back at the box office but already have 1 new screenplay in production and have been contracted to write several more; meanwhile the screenwriter of Crazy Rich Asians (which not only outgrossed Morbius but nearly grossed as much as Morbius' screenwriters' other films combined) has only been hired for a single film (Raya and the Last Dragon) since.
And the point is that while she had a major blockbuster success, this will only be her second film since that success; in that time, the losers behind Morbius will have worked on 4 films.
Also, Lim lists herself as a director of the film in her Twitter bio[0], so it seems like a lot more than a maybe at this point.
[0]: https://twitter.com/adeleblim?lang=en
Separate from all that, I don't understand your larger point about Lim. She went from Crazy Rich Asians which grossed over 200 million, and then went directly to work on Raya, which grossed over 100 million, and now is directing and producing her own movie with hand chosen writing talent. Where exactly is she struggling? And where are writers being forced on her?
How many other second-tier directors who could make great films are out there not getting funded?
I don't know, how many? Your example of Daniels is interesting because Daniels were discovered, so it doesn't help me understand how many people are out there that could do a great job but don't have the opportunity.
I've consumed a lot of amateur writing, music, and comedy. Most people just suck at creative endeavors. On the other hand, I once saw the most beautiful performance by a girl busking on the street. Fast-forward a few years, and now she's doing world-wide tours constantly and has a great musical career. With YouTube, Twitch, Spotify, and TikTok, it's never been easier for talented young artists, writers, and directors to rise up from obscurity.