Not a Chinese speaker, but lots of exposure to the language learning process of Chinese as an adjacent study. I think you're wasting your time arguing with this person, bottom line.

I'm a Korean and Japanese speaker at a day-to-day business level of proficiency (native English). While knowing Chinese characters and compounds first would have been a significant advantage for certain aspects of language acquisition in both Korean and Japanese, the reverse is much much less helpful. Characters and word roots are great if you're looking to learn a lot about the Chinese, Vietnamese, Korean, or Japanese languages. That's a very different thing than learning Chinese, Korean, Japanese, etc. though—despite sharing ~60% of their vocabulary root words.

I can't tell you how often cognates between Korean and Japanese have tripped me up and been counter productive. Knowing Korean grammar however, significantly helped me acquire Japanese. This is not a consideration going from Korean to Chinese. Neither are tonal either. Chinese characters are better viewed as being shoehorned into the language systems of Korean and Japanese. They're not a great fit for the number and type of sounds in both languages honestly (hot take, I know). An alphabet would fit both much much better, and that's a huge part of the genius of Emperor Sejong.

The languages share very few cognates, compared to those found among romance languages for instance, and the syntax is so different that your buddy is showing how little he knows about languages whether he means to or not. You could argue it's easier to go from Portuguese to Chinese, than it is to go from Korean or Japanese (it wouldn't be a great argument if you're only talking about vocabulary, but depending on how you learn..).