If you have the luxury of owning a III and a FM3, or two IIIs, do a comparison for yourself.
For example, select the CCV 2B on both devices, stock settings and the same cab IR, and note the difference in thump / chug.
Compare the difference in attack of the Tucana Lead where the new version sounds more natural.
Try the AC20 EF86, just because it's so good.
Blow your mind with downtuned FAS Brootalz.
Compare the stock Brit 800 and hear the difference in dynamics and realism.
And select a Fender and hear more amp-in-the-room as before.
To some, the changes may sound minor in the beginning, especially when you can't compare old and new directly. But the improvements are there, even if it may take some time to recognize them.