That is the thing, from phonetic point of view every letter has its own sound which is not interchangeable. In the word god the letter g is making /g/ sound so you read it as it is written in word gentle it is not making /g/ sound so you read it differently than it is written. That is why there is phonetic transcription. In Czech for example there is no need for transcription to be sure of pronunciation of Czech word as sounds of letters are always written as you read them, unless you talking about nasal consonants and vowels, alveolar vowels etc. but they come with structure of the word so it comes naturally to the pronunciation. There is of course phonetic transcription in Czech , by IPA standards or by Czech system, but you don't need it to actually know how to pronounce the word when you already how to pronounce letters. I understand your point of view but from linguistic perspective it is just not correct.