Zlatko said:
Sure, it's not an improvement because of the reduced 35mm of range ... if focal length range is your measure of improvement. In that case, 10X or 20X super-zoom would be the ultimate improvement. But focal range is not the usual measure of improvement. The facts are as shown by the numbers in ahsanford's post above. Those numbers clearly show an overall improvement in IQ.
Of course, owners of the 24-105 aren't "throwing it out" to buy this 24-70. That doesn't reflect on the 24-70 at all. The 24-105 is a fine lens in its own right and remains a good value. So no one is crazy enough to throw it out. The 24-70 is an alternative with some improvements and differences, not an obvious replacement. Many people will find the 24-105 meets their needs and budget better. That doesn't mean that other people won't find that this new 24-70 meets their needs and budget better. That's the beauty of alternatives. They meet the needs of different people with different needs and applications.
Optical perfection is a very high standard. You don't get it for an extra $400-$600 from any manufacturer.
That's the problem.
Your logic clashes with the reality of facts being that this lens is going to replace the 24-105 as FF kit lens. And I can see why people react with a loud WTF.
Also, achieving optical improvements at the expense of zoom range is hardly something to rave about. At its best, these two lenses are equal. Then why is the new one supposed to cost so much more?
By the way, this lens is also hardly any sharper than the Tamron 24-70 @f/4 - which is one full stop faster, if you need it.