It's best not to think of Hanyu Pinyin as using "English characters" to pronounce Mandarin. It's just a mapping of the initial, medial, and final sounds onto the Latin alphabet in a consistent way, so that once you know the mapping, you know the pronunciation right away, and more practically, you can _type_ it right away.
I used to always think these romanization schemes were really bad, until I realized they were just not for me. The ease of sight-reading and getting the correct pronunciation for a random english speaker is not the goal. It's primarily for the convenience of users of other languages to have a systematic encoding. To make it pronunciation-friendly you would have to have to add a bunch of complexity to the mapping that would compromise its usage by the real audience.
https://en.wikipedia.org/wiki/Pinyin