Really? Why is everything called "radical" nowadays? The "radical left" who want healthcare for everybody, the "radical right" who oppose immigration. Radical egalitarianism? Really? Because they don't want to fund programs for gifted kids? You may not like it (I myself am ambivalent and the best solution is likely in the middle), but it's not "radical".
It's radical because goes against all evidence, experience, and common sense - it is ideology taken to a puritanical extreme. There is no more extreme position one can take.
And even if that was the argument, the term was used in the context of "radical egalitarianism". So, the argument doesn't automatically transfer to such a radical variety of "egalitarianism" in society as a whole if it focuses on a single aspect.
There are two levels of quite extreme exaggeration here, calling the end of a particular school program "radical egalitarianism". Which words should we use if an actual radical proposal comes along?
Given that, there's nothing else to save the word for. This is the limit; the max. So if radical refers to anything at all, it refers to this.
There are many things I can imagine that are much more radical than this. Everybody has to live the same, wear the same, eat the same, think the same. That's pretty insanely dystopian for sure, but much more egalitarian than barely mixing kids of different ability in the same classroom.