Random mutations yes, but also in natural selection which is absolutely NOT random.
I'm not sure what this proves. It sounds like in your analogy the sentence is a genetic sequence and each letter is a gene. However if that's the case it doesn't make sense because you can change a single gene in a genetic code and have a great effect (positive or negative). Thousands of diseases are caused by a single gene. Additionally there is a perfect English sentence but there isn't a perfect genetic code. If you start with a random assortment of letters and do enough random mutation you absolutely could get a perfect English sentence but you are trying to take something that is perfect and make it more perfect. Of course that's impossible.