In the older Wade-Giles system, they indeed tried to maintain some similarity with how English uses the Latin alphabet. Ch was used, for example Ssu-ma Ch'ien,

In the older Wade-Giles system, they indeed tried to maintain some similarity with how English uses the Latin alphabet. Ch was used, for example Ssu-ma Ch'ien, which is now Sima Qian. Using Latin q for a ch sound isn't unheard of in European languages, for example, in Albanian. Mandarin pinyin is "rational" in the sense that any other language with phonemic values for the Latin alphabet widely divergent from Latin or English, like Turkish, Albanian, or Irish.