Roman letters works somewhat with English because they are both phonetic. Japanese is phonetic too, they have an entire different hiragana alphanet with all the sounds of their language. There is no word in Japanese that you cannot sound out with that alphabet. In Chinese every symbol has a sound, a Chinese sound. Not sure how much you understand about Japanese but you can't just derive the pronunciation of a new word just from looking the components.

I do agree that English is terrible too. English is a mess of Latin, German, French words which is why spelling bee competitions are a thing in English but it would be stupid to have them in other languages such as Spanish and in fact Japanese too. In Spanish you can spell any word regardless of how long and confusing it might seem. Japanese too, using hiragana you can spell the sound of any Japanese word regardless of how how long or rare it is, good luck writing it though, a Japanese spelling bee is not possible but a written one is.

My argument is that the Japanese writing system is a big mess but spoken Japanese is not. Spoken English is a mess too. Any language were you have competitions about who can spell and write the words of the language is a big mess of a language.