Dave, let us use some of your Gnomian logic on Macmillan's line,
" A new generation of British historians, among others, has done much to explode such lazy generalisation and show that commanders developed both strategies and tactics that, in the end, worked."

She does not qualify "A new generation of British historians," with "some," "many," or "most."
She obviously would if she did not mean "all."

As an historian of WW1, it is her job to read them all.
It is possible we all might have missed one, but not her.