The missing part of mathematics education, IMO, would be to focus more into developing the intuition of what something means, instead of the current focus on getting some (numeric) results.
You can't just skip arithmetic drills in favor of intuition and still come out with students who are prepared for further study in math. There's a reason Kumon etc are so popular - parents are replacing the lack of mathematics drills in schools with after school options, leaving behind all of the kids whose parents can't afford it.
And there still are arithmetic drills, it's just not the only focus in early math education.
Kids can absolutely learn complex concepts early, they just may not be able to formally write them out until a few years later. But they’re kids, so who cares? By the time they need to be able to write out math equations, they’ll understand the underlying concepts on such a deep level that it doesn’t matter how long you make it, they’ll plow through it.
I was a skeptic, and am aware that I sound like a cultist, but damn if Montessori isn’t something special. I highly recommend it.
0: https://www.montessori-theory.com/montessori-trinomial-cube/