I've never experienced or witnessed a scenario in which trying to support varying levels of experience didn't result in lowering of standards. People with the right interest and capabilities will strive to clear the bar and will not expect the bar to be lowered for them.
You may not know this because Harvey Mudd College is a small school, but it is extremely rigorous (not quite MIT/Caltech, but pretty damn close). Their middle 50% of the admitted students' math SAT range is 770-800[0]
I would be extremely surprised if HMC had any bar-lowered classes.
Just because you offer both a linear algebra course and a course on groups and rings doesn't mean the linear algebra class is some kind of mickey mouse credit--it's just for people who haven't seen that material before.
There's the "math majors' math track" and the non math majors' math track at most institutions. Even within the majors track, there's separation between experience levels and intended tracks within the discipline. Ex:
MAT215-217: Recommended for math majors, some prior experience in constructing formal proofs is useful but not required.
MAT216-218: Accelerated math major sequence, for students with substantial background in university-level proof-based analysis courses.
MAT214-204-203: Alternative path to majoring in math, with a more algebraic introduction to proofs
MAT203-204-215: Alternative path to majoring in math; good path for the applied math certificate.
But the difference in your case is that we don't expect, nor care, whether math majors and non-math majors end up at the same destination. It's okay and expected that math majors will end up learning more and becoming better at math. But when we're talking about people studying the same major, then this is not okay. You will either end up slowing down the fast track students or you will give them an advantage over those that weren't on the fast track.
I disagree with your premise, since our current situation is that different students in the same major _already_ end up in different levels of aptitude by the end of their studies. Some far exceed that of the typical student.
Preserve the ability for those with this level of prior experience or aptitude to thrive, while providing support for those who do not have this head start but could either (a) Catch up, given the right initial environment and ramp up, or (b) never catch up to the most well equipped students, but will still be proper graduates of the program.
Which is why they're creating separate tracks rather than trying to cram everyone into one class.
The people with prior experience can take classes that are suited for their level, and will be challenged rather than bored and resentful of their classmates.
The people without prior experience can ALSO take classes that are suited for their level, and will be challenged rather than intimidated and condescended to by their classmates.Once they have some experience, they can move on to the other classes.
It's a win win for everyone, including the people who through whatever luck or drive have experience before they enter the system. Remember, not everyone has the same access to things like books, computers, and programming classes in earlier environments like high school. Making an actually introductory path helps level the playing field without lowering the bar.
