The contrast between stressed and unstressed syllables dictates the rhythm of a sentence in English. Thus, it's a stressed timed language, meaning the interval between two stressed syllables is approximately equal. As a result, both vowels in unstressed syllables and function words, such as auxiliary verbs, tend to be neutralized with a short vowel sound called schwa, denoted in the International Phonetic Alphabet by the symbol /ɘ/, which is the trademark of the English language. Consequently, that phenomenon causes a loss of vowel identities and makes the language more difficult to acquire for non-native learners. Furthermore, all the contractions exist to fit that prosodic characteristic of English. 聼起來自然嗎?

First of all, you have an excellent command of English, parabéns! Assuming the content is correct, I would only change a few things with regard to grammar and style:

The contrast between stressed and unstressed syllables dictates the rhythm of a sentence in English. Thus, it is a stress-timed language, meaning the interval between two stressed syllables is approximately equal. As a result, both vowels in unstressed syllables and function words, such as auxiliary verbs, tend to be neutralized with a short vowel sound called schwa, denoted in the International Phonetic Alphabet by the symbol /ɘ/, which is a hallmark of the English language. Consequently, this phenomenon causes a loss of vowel identities and makes the language more difficult to acquire for non-native learners. Furthermore, all contractions exist to fit this prosodic characteristic of English.