1. That Chinese writing is inherently inefficient. It's actually very efficient...to read. And nothing beats the efficiency of having a script that maps perfectly to the language. Also as sibling comment notes, UTF-8 is a thing.
2. That there is no relation between written characters and phonetics. Incorrect, as several sibling comments point out.
3. That Japanese kana represents a successful "modernization" of kanji that Chinese should emulate.
4. That Chinese is "basically kanji" - assuming the Chinese and Japanese languages are essentially interchangeable. They...are not. I can't even begin to emphasize how much they are not. Chinese is subject-verb-object while Japanese is subject-object-verb, for instance. Chinese also has many phonemes that are incompatible with Japanese, which would not be covered in hiragana. Finally, kanji came from Chinese and has subtle differences and while it is mostly a subset of Chinese hanz, it has its own slightly different character set