I do agree that there can be a problem with self publishing quality, spelling errors, typos, etc. But even ebooks released by many traditional publishers are plagued with these.
As far as traditional publishing being gatekeepers that create quality by only letting good books be published, I don't believe that is true.
Their record is spotty.
Traditional pubishing rejected many authors who are now successful including Agatha Christie, J.K. Rowling, Louis L'Amour, Dr. Suess, Zane Grey, CS Lewis,
and many others.
I think that self publishing is great because it lets authors publish more easily and reach readers. Success will be based on how much people like the books and want to buy more rather than your book being rejected for bogus reasons.