Thus, the final binary can be recreated from those tarballs just fine, because *technically* it's the full Emacs source code all right. Legally, though, it's not, because of the definitions in GPL.
Not so. If what you seem to be implying were true (that there's no ethical problem with this, just a legal one because of the wording of the GPL), people could simply compile their source down to assembly and distribute the "source" that way. The final binary could be created from the compiler-generated assembly just fine, but that's not the issue here. The goal of the GPL is to prevent distribution of any generated machine instructions (in any form or language) without distribution of the original (in any form or language).
This is exactly the kind of behavior that the GPL was intended to prevent.