French and Spanish, as romance languages, have a lot in common but they are separate languages. Writing Cantonese in standard written Chinese is similar to asking Spanish speakers not to write phonetically, but to rather write in French.
The American Mandarin Society has courses for Professionals. I guess they make quality judgement on what to keep or throwout in use of the Chinese language in their curated walled garden for snooty State official use.
As characters are not married to pronounciations, both old (i.e. classical) texts and newer memes can be hard to understand or misunderstood despite knowing all characters. Guesses are often close enough, which is a feature of the logogram.
Out of curiosity, do you speak a variety other than Mandarin? And if so, do you think you'd be able to find "proper" characters for everything you could say, like pishpash did above?
The matter isn't whether I can find the proper character for everything you could say, but rather whether the spoken variety themselves can be based on written characters. In the example case you gave, it does.
The spoken varieties of Chinese can still be mapped to a set of characters, that still means there's a commonality underlying all of these variety. For instance, Beijing dialect/slang "颠儿" means '(he/she) is gone', which wouldn't be readily apparent or understandable to even mandarin speakers. but the first character has the meaning "run/trip".
Old dictionaries list 颠 as a synonym of 顶 only, without a "run/trip" meaning. Most likely the character was only used for this word because both are pronounced "diān" in Mandarin and people didn't bother to make a new character, e.g. by combining [足颠]. The -儿 suffix is also interesting, because the sound modification it represents is something Beijing Mandarin speakers picked up from the Manchu during the Qing dynasty, it has nothing to do with the meaning of 儿. So 颠儿 is a relatively new addition to the written language that is not shared with non-Mandarin varieties.