Well, IOR has a 6x zoom range and their optics are pretty darn good, and the 7x zoom range 4-28x56 suffers none of the optical shortcomings that the you mention wwhen compared to the 4x siblings.
I am not a scientific optical expert, but I do have the ability to tell good glass from great. Even if bushnell did not change the optics, from the 4200, the limitations that you mention results in a compromise in the optics to the enduser.
However, I beleive they did not use the 4200 glass. Why? Because they don't say so in any literature on the scopes. Would they not boast, "the brightest scope in the world, AND the widest zoom range??"
Thanks for the link, you can't ever learn too much.
"See Better, Shoot Better"