This just appeared in the latest SUCCESSFUL HUNTER. Written by a very well respected and experienced African PH. Finally, someone willing to state the obvious.
1. "Modern premium bullets make the 270 Winchesterstandard cartridges into the all-around plains game cartridge."
2. "If something is more than 350 yardsfurther away than the Hunter knows from experience he can kill I contend no one has any ethical business shooting unless the game is wounded."
3. Too many clients are arriving overgunned and under practiced.
To me these make more sense.
As has been pointed out, modern premiums create a "high tide effect" increasing the effectiveness of ALL cartridges. 'Standard' is vague I know, but most will know what is meant... 270/280/7RM/308/30-06...
I have witnessed hunters who had no business taking shots at game farther than the end of their barrel. Point of #2 ought to be, IMHO, along the lines of the classic, "a man's gotta know his limitations." For instance, I have no doubt that Darrel Holland can make an ethical hit at longer distances than me, whether all things are equal or not.
I have also witnessed hunters who had no business taking shots at game farther away than the end of the barrel who thought that a mag, super, or UBBER mag, could remedy the issue. That is to say, I have no doubt that #3 is true.
All that having been said, the author cited in the OP has a lot more credibility than I do in making such proclamations.
That is to say, I have no doubt that #3 is true. 
