Personally, I'm not convinced that risk capital is really that beneficial for writers. The vast majority of aspiring writers either don't finish or don't write something people want to read. (I don't mean that to be harsh, it's just that good writing is very hard and since there's so much of it already out there, competition for the reader's time is fierce.)
At the same time, the capital needed to write is virtually nothing. All it takes is time. Editing, proofreading, and cover design are legitimate, important costs, too, but even those aren't that huge. And they only come into play once the book is written, which means most won't reach that threshold.
I, of course, want great writers to be able to devote all of their time to that and not have to work a day job. But I think having to write your first book or two in your "spare" time is an acceptable way to separating the wheat from the chaff.
In other words, write a book or two in your free time. The money you get from those will be your risk capital for your next work.
There's really no need to talk about "enough", "acceptable", etc.
It's very simple - if there's less money available for a first book, less people will do it. This means that there will almost certainly be less authors, therefore almost certainly less great authors (though it's probably not linear).
Not to say you're wrong, just that talking about "I think it's sufficient" masks the fact that it doesn't matter what you think, there will in effect be less great books written.
There's already very little money available for first books, relative to the many many people who give it a shot. I've worked at a number of publishers and trust me, the "slush pile" is always huge, always growing, and always hopeless. The other poster is correct that most writers will never finish, but more than enough still do.
Angel investors and incubators provide basically the same service, but rarely for books. I wonder why that is? There have been a number of books/series that I can think of that have spawned $100M+ valuations - Harry Potter, Hunger Games, 50 shades of gray, Jurassic Park, Song of Ice and Fire. If you include comics, then the list just goes on: Superman, Spiderman, Batman, X-men, Watchmen, etc.
