But you would still have the "as applied to a particular aspect ratio" problem.
That is at most a reason to provide that angle info in the product description but not engraved on it -- just as is done with the "35mm film camera equivalent focal length". But in practice, these days most lenses are used on cameras in the formats for which they are intended; the "crop" issue is mostly restricted to lenses designed for medium format film cameras, now that "APS-C" and Four Thirds cameras are overwhelmingly used with lenses designed for those formats.
For example, the common wisdom is that 4/3 and m4/3 sensors have a 2x crop factor.
That might still be a somewhat common misconception, particularly amongst old-timers who are still most familiar with the 36x24mm format (which most photographers these days are not). But it is at best an anachronism and at worst wrong, since there is no 2x crop involved, except in the rare case that a lens designed for 36x24mm format used via adaptor.
But because the 4/3 and FF or APS sensor aspects differ, it is 20mm lens, not a 17.5mm, lens on a 4/3 camera gives the same vertical field of view as a 35mm "FF" lens
These variations in aspect ratio cause only a modest variation no more than about 10%, and this imprecision applies equally to all the proposed numerical measurements, be it a fake focal length an angle, or a magnification factor. In practice, I doubt that the small variation in the number will cause any real problems: lens choice will always give only approximately the desired field of view, to then be adjusted by changing the subject distance or cropping or zooming or such.
However this imprecision is why for most purposes, I prefer to avoid the false air of precision given by numerical statements like "105mm" or "23%" in favor of more honestly imprecise descriptions like "medium telephoto". Maybe "about twice normal" is sufficiently imprecise.