Do all students need to be equally good in all subjects? Standards for aircraft differ based on what a plane is going to do. Why not for students? Proficiency might be enough in math for a student heading into the arts. It would surely be too low for one aspiring to an engineering career.When every Eduwonk, Administrator and Reformer is equally good at Calculus, Physics, Shakespeare, writing, Biology, History, Art, Music ... then we can expect that every student will be proficient across the board.
I'm not saying we shouldn't teach them everything, but we can't expect total proficiency.