Ideographs aren't great for languages where the same word is written differently depending on the tense, case, person, etc (like English '-ed' for past tense; 'is' vs 'was'). They're good when you have a distinct word for expressing those things (like English 'will' for future tense).
The Hiragana syllabus was developed to write the grammatical parts of words. It was developed by taking existing Chinese characters, just like you described with Akkadian, and simplifying them to make them easier to write. Many Japanese words will contain a mix of writing systems, with the root of the word written in ideographic Kanji and the grammatical conjugation written in syllabaric Hiragana.
And there's also Katakana which is a syllabus of even further simplified characters derived from Hiragana, which is used for writing loan words not derived from either Chinese or Japanese.
It's of course a bit more complicated and messy than just what I described, but that's the gist of it.
Most also imagine that non-Mandarin Chinese languages are just dialects of Mandarin with "pronunciation differences", not full-fledged languages. They read texts written by, e.g, Shanghai speakers, and do not realize that the text written has been translated to Mandarin. Most people speaking another such Chinese language are not literate in that language, and rely on written Mandarin, translating as they go. This happens even on nominally "local-dialect" forums.
Of course all this has deep political implications, so is not safe to discuss there.
Cantonese seems more a hybrid language akin to English in that it is a blend of Tang Chinese during a migration of Chinese from further north and the language(s) of people already living in that area.
The Cantonese description of the entire Chinese ethnic group is literally the Tang people. It applies to all of what is considered subgroups including Teochew, Taisan, Hakka, etc...
Cantonese definitely shares similar pronunciations for certain basic words with other Chinese dialects/languages.
Also, Cantonese is just one language in the area. There are other dialects that preserve Tang Chinese pronunciation more clearly and are closer to Mandarin. My Chinese surname in my dialect sounds exactly like it would in Mandarin but not in Cantonese.
Supposedly Cantonese is actually closer to Tang Chinese than Mandarin because operas/poems from Tang times still rhymne in Cantonese but not Mandarin. This is supposedly due to language drift rather than them not sharing some common ancestry.
Think more of the Norman invasion and how German (proto Viet and who knows what else) merged with French (Tang Chinese) to create English... and then suppose England and France would periodically merge and separate instead of splitting apart decisively after the Hundreds Year War.
Thus Cantonese and the other similar languages are definitely full fledged but there is also some shared ancestry with Mandarin. Also there is a long, long history of a common written language.
People may wish to highlight one aspect or another. Is it English or French if the histories are much more intertwined? Does that question even make sense or is asking that question mostly political?
Someone else may have more knowledge of origins of other Chinese dialects/languages.
Similarly, there is a Sinitic family of languages. But they are as different from one another as any collection of languages that have evolved away from one another, and mixed with other families, over millennia.
It is common for Chinese to believe they can read texts from 2000 years ago because they recognize the signs, but what they think it says has at best a tenuous relationship with what was written.
1. Cantonese recognizes the Chinese as a common people and have a word for it. The word isn’t just used historically but is used to this day. The French don’t see the Italians as fellow Latins much less call them that.
2. There is a continuous use of a single written language. It isn’t about reading text from 2000 years ago. It is communication even within a subgroup using the same written language. One job people had not so long ago was to write letters for those who were illiterate to communicate with family and others far away. My grandmother did that.
Sinitic influenced cultures invented their own scripts: Japanese hiragawa, Korean Hangul, Tibet has had its own script. Vietnamese may be the closest, having adopted their own recently.
The French use the French written language to communicate with each other. The Germans use the German written language to communicate with each other.
3. Furthermore, there are continued common cultural traditions expressed in that language (classics) and practiced to this day (Chinese New Year, tomb sweeping festival, moon festival, etc…)
4. Whereas other people’s recognize some of those traditions as coming from China (Art of War) and as coming from another group, the Chinese have always seen them as their own.
This is the case with both people speaking Mandarin as well as Cantonese. My high school classmate would read the Art of War. He spoke Mandarin. My grandfather many decades earlier would read Chinese classics. He spoke what is often called a dialect of Cantonese. Both felt that it was a core part of their cultural inheritance.
The English celebrate Newton as their own. Some French may think highly of him but they don’t recognize him as French.
5. There is this misconception that China was a bunch of disconnected cultural groups till recently. That wasn’t the case. My grandfather from southern Chinese went to a university in Beijing. This was roughly 100 years ago.
I wonder how the various imperial ages of China controlled their empire? I wonder what written language the imperial exam system was in?
6. Also, group affinity in China is far more granular than you think. It isn’t first Cantonese vs Beijing. It is first what is your ancestral village.
You seem to want to look at the distinctions but don’t want to look at the common identity. Whether someone sees another as part of the group or not, these groups have a lot of shared and continuing culture. There are definitely groups in China that don’t have this share this common culture but that is to ignore the many that do. The reality doesn’t seem so clear cut to me.
I don’t know much about the other subgroups in China beyond the several I grew up with and encountered. Perhaps they are different but it would be far more enlightening to hear from people actually from those areas. It would be doubly interesting to hear of the perspectives of their grandparents.
My remarks were solely about local languages.
We can talk about Chinese political unity up into the modern era, but the shared cultural legacy goes back to the classical period, mediated by traditional literature originating in 14th century. Mandarin has long been the language of imperial administration, and has exerted a regularizing influence on local languages without displacing them. Still, it is certainly a very different language from that used to administer empires many centuries ago, despite relying on a common written syllabary. Meanings drift.
The original topic was how people who speak only Mandarin are taught that other Sinitic languages are "just dialects", and are misled by seeing users of these other languages writing in Mandarin, translating as they go; and not understanding the depth of translation involved. This confusion between translation and mere transcription does not seem to occur outside China. The current government prefers the confusion, probably to help enforce a belief in more unity than exists.
But do they have a flag?
You may not have intended to impute intentional deception to someone, but that is what you did, and it's offensive.
I'm with macintux. I think that was rather rude. Nor do I think macintux was patronizing.