But why should the bright students then expected to do the 'deeper understanding' that no one else is doing?
The bright students should be doing something that the other students aren't doing, shouldn't they?
In English you would certainly expect them to have a deeper understanding of texts read than other students.
If you want to see what 'deeper understanding' looks like in maths, the Further Maths GCSE is pretty good. It has a lot of questions of the 'Miss, you never taught us that' type, where you actually need to figure out what to do.
Having to figure out what to do themselves is actually a big problem in maths. Kids see a 5 mark question that they don't know how to start and just skip it. We even see it as an issue at A-level. In the statistics module, what you need to to is given to you 'Calculate the equation of the regression line....'. In mechanics, its 'Here's a scenario, calculate the force at which the object hits the ground'. Guess which they struggle more with?