For an English speaker to be able to pronounce Chinese words, it would certainly be a better system. However, the main purpose of Pinyin is not that, but to indicate pronunciation for native Chinese speakers (most of whom had little exposure to English or other foreign languages when they learned pinyin, of course nowadays it might be different as kids start learning English at a much younger age) and to teach in schools. Using a Latin alphabet so that it's easier to integrate into international systems is a consideration, but never the main goal.
Besides, Chian Shuesen sounds closer but it's still not the same. Approximation has to happen somewhere, and there are already ch-/q- and sh-/x- distinction within pinyin.
One gets used to pinyin really quickly.