Good teachers unfettered by standardized course plans, when dealing with brilliant students, keep pace with and support those students. If this attracts even more brilliant students, all the better! Then the brilliant students will also support and motivate each other leading to even better outcomes. This is an ideal situation unless you're one of those Harrison Bergeron people who wants to cap high achievers so they don't leave the dummies in the dust.

We really should be prioritizing the brightest students, because their brilliance has the best payoff for all of society. Better to have 100 students who are genuine math wizards and are prepared to continue building on what they know than to have 10000 students who sort of learn basic calculus then forget all of it, with those previous 100 lost in the noise and never given the resources to reach their potential.

On the contrary, standardized course plans are actually the most effective way to provide truly reliable instruction at all levels in a mass lecture/group education format. One key reason why those 100 math wizards don't all become PhD's is that math instruction at both school and university level leads to the proliferation of random gaps in learning where some content just wasn't reinforced effectively. Since math instruction generally builds on previously-learned math, once you accumulate enough of these gaps you hit a wall, and will need remedial instruction (often sought via autonomous self-teaching, of course) to make any progress. The dynamic is structurally the same between the "dummies" and the "math whizs", all that changes is the level at which the problem arises.

Focusing on a standardized course plan that the student is able to learn, memorize and ultimately repeat effortlessly makes it easy to ensure that absolutely everything was reinforced properly.