To stretch the book analogy beyond breaking point, it would be like if Patrick Rothfuss released The Name of the Wind, and JK Rowling immediately put out "Harry Potter and the Kingkiller Chronicles, now with added Kvothe", and basically used her name and the Harry Potter brand to outcompete Rothfuss selling the same thing. (Obviously for books, you've got copyright, but there's no copyright for your favourite app idea.)
I think the extent to which that is actually true is hard to say, but I think it's a different point to the one you're arguing against here.
A wise friend of mine once said, in regard to "ideas are nothing; execution is everything": you can tell a thousand artists to paint a portrait of an Italian woman with a countryside landscape behind her but, good or bad, none of them are the mona lisa.