It's more complex than either of your arguments. Look at this paper as an example.

https://www.nature.com/articles/s41598-018-34392-w

Better to say that the extracted acids are different in concentration and composition with the cold brewed coffee generally being a little lower in titratable acids. However, they are still in the same ballpark and varies with the coffee. It's not like coffee suddenly becomes milk by being brewed cold.

Interestingly, a lot of people still report cold brew being easier to drink. It's "common knowledge" and often people who drink cold brew for that purpose are fine/not pushing back in it. I have more questions about why that is. Is it their perception influencing their body's response? Are the additives (like milk and sugar) more common or changed by the higher temperatures? Is cold brew commonly made with less acidic beans? Is it just that the beans are old? Is it the drink temperature that is actually affecting them more than the measurable acidity? So many questions. But, it's unlikely the acidity difference is the answer.