Agreed. Though I think there is a missing nuance among the existing libre licenses.
Benjamin Mako Hill has suggested finding an alternative name for this nuance such as "Libre Ideal License" (Our aim is to produce a definition and license which represent "pure" freedom - another option for those who aspire to such ideals).
So, if we agree on a name for the license, let's say "Libre Puro License" for this discussion, then CC-BY and CC-BY-SA would both be "libre licenses" in the sense that they do not violate the 4 freedoms.
CC-BY-SA would be "Libre Puro compatible" - meaning that "Libre Puro" works could be modified or incorporated into another work and the result licensed as CC-BY-SA because CC-BY-SA perpetuates the freedoms (via SA).
CC-BY would be a "libre license" but not "Libre Puro compatible" since it does not ensure freedom for future derived works (or uses of the work in restrictively-licensed collections, etc.).