That just means that we need to move the bottom 20% of students into their own classes where they can get the extra attention they need. That means they can get a high quality education and so can everyone else. You do not have to choose. You can have both.
No, you do have to choose because money for education (or anything) isn’t unlimited.
There’s a real question of how many resources and what kind of ROI you’d get from trying to educate that bottom 20% to the same level.
I saw this play out when I was in school: profoundly intellectually disabled students getting 1:1 or even 2:1 teaching, trying to get an 18 year old to be able to read 3 letter words, while AP classes were bloated to 30+ students.