Guthries books are deeply flawed due to the large number of of factual errors, lack of proper footnotes and the authors choice to deliberately ignore modern research on the subject. Significant parts of the books are sheer fantasy without any foundation in historical facts and can only have been made up by the author.
For example he describes in great detail how the Green brigade fought with the "Neu-Pappenheim group" [sic]at Breitenfeld. Not only was the Pappenheim regiment never known as "Neu-Pappenheim" in any period source, but it and the other regiments in the group took no part in the battle at all due to having got lost in the smoke and dust during Tilly great wheel. As this fact is clearly spelled out in works which Guthire lists in bibliography. He has either not read them or has ignored the sources in favour of his own fantasy creation.
A second example is his description of the Swedish commander Johan Baner.
Baner is described as "commoner" who has risen through the ranks and who was "obsessed" with his lack of socal status and therefore regarded his superiors with "paranoia" and his subordinates with "contempt" and "distrust". Baner was also incabale of cooperating with anyone except Torstensson.
In reality Johan Baner had been born into the highest levels of the Swedish nobility, the Baner family was both old & powerfull with seats on the Royal Council. Hence the claim that he was obsessed with his lack of social status is without any fundation at all.
Baner had never served in the ranks as he began his military service a a Cornet in the Hovfana (Horse guards).
The description of his relationships with subordiantes & superiors is equaly false. While there was a fair amoutn of friction in several of Baners realtionships it wwas nothign unusal for the period and Baner was actually noted for his skill in gettign along with his subordinates (officers & rank and file alike) in some very diffcult situations.
These major errors are just the tip of the iceberg.