US students are expected to be able to read 104 characters by the end of 6th grade. While Chinese students are expected to be able to read 20k words by that time.
Characters in Chinese can be combined to make more words, and you need around 9k words in English to read a novel and 2k characters in Chinese to read a novel.
It is wrong to compare number of characters in English to number of words in Chinese. The proper comparison would be words in English to words in Chinese. By 4th grade I knew enough English to proofread ycombinator posts. Of course, that is a low bar...
And I think you're off by an order of magnitude about vocabulary size. Chinese vocabulary size around 6th grade is more like 2K - 4k words tops, not 20K. See
https://www.guavarama.com/2015/02/06/chinese-characters-by-g...
I get that there are tradeoffs and that logographic languages have advantages and disadvantages.
In this case specifically though there seems to be a pretty strong consensus that one of the advantages of a phonetic alphabet is ease and time to learn.
In a completely phonetic language (which English is obviously not) once a kid learns the alphabet and around 50 phonemes you can represent with it, their auditory and reading vocabulary is roughly the same. So you can have 6 year olds with a reading vocabulary of 20k words.
It’s not that simple, but clearly the more phonetic a language is the easier it is to learn for someone who can already understand the spoken words.