In order to teach everyone the same thing you can only teach as much as the stupidest and least motivated person can grasp.
If all (e.g.) 7th graders must have the same knowledge of math, that knowledge of math cannot exceed the knowledge attainable by the dumbest (read: any) 7th grader. This is tautologically true.
What is your solution to enable high quality curriculum and ensuring uniform success?
What did you mean by equalize life outcomes then?
again, what is your position and proposal?
The only noteworthy difference is defining acceptable failure rate, which neither of you did.
2) Can no student advance until everyone has mastered the material?