Pinyin's existence is as a stepping stone, and misses out on a lot of interplay between words. Pinyin negates how you can separate Chinese characters into different symbols, such as the Chinese character '鮮' ('xiān' in pinyin), is the combination of '魚' ('yú') and '羊' ('yáng'). It's certainly not impossible to learn Chinese through pinyin, but it would be an odd choice.