I don't think one can reasonably claim that in English "words are mostly pronounced how they're written". I mean, "i" can stand for /i/, /ɪ/, or /aɪ/, for example (and also for /ə/ if you don't count "ir" as a distinct grapheme). Although vowels at least (mostly) follow some predictable patterns based on syllables - but e.g. it's impossible to say whether "ch" stands for /k/, /tʃ/, /ʃ/, or /x/ without knowing the etymology of the word.