I advocate teaching less due to many primary skills being glossed over. I prefer kids who have the ability to read, write, do arithmetic, think critically and work well with others. We're too busy trying to get every kid to graduate college early to focus on these skills.
But we aren't and it seems like you just made a backdoor argument for why we shouldn't have advanced classes.
It might seem that way but I'm a teacher who loves and specializes in mathematics. I teach Adult Education and see many 16 year olds who can't do basic multiplication or read above a third grade level. Employers in my area ask us to teach them to play nice.
Ultimately I wish we could master those skills earlier allowing us to drill down into more complex topics. Instead us teachers teach to a test. I'm guilty of this as well. I wish students had more enriched activities including the arts and were more educated. To me it's about priorities.