You're right that children's books can be excellent, and for generic topics a well-reviewed book from a skilled author and illustrator will beat what we generate. No argument there.
Where we see real value is in the gaps the publishing industry doesn't serve. Bilingual families who can't find books in Maltese/English or Estonian/German. A child with an insulin pump who wants to see a superhero like them. A kid processing their parents' divorce. A child with two dads, or being adopted, or starting at a new school in a country where they don't speak the language yet. No publisher will print a run of one for these families - but these are exactly the stories that matter most to them.
On the UX points - you're right on both. We should localize the showcase to your language, and the signup wall before trying is too much friction. Working on both.