Ferguson, the author, backs it up with statistics.

"As Table 32 shows, the greatest of all the paradoxes of the First World War is that, despite being disastrously disadvantaged in economic terms, the Central Powers were far more successful in inflicting death on their enemies. According to the best available totals for wartime military deaths, some 5.4 million men fighting for the Entente powers and their allies lost their lives, the overwhelming majority of them killed by the enemy. The equivalent total for the Central Powers is just over 4 million. The Central Powers' superiority in killing was thus of the order of 35 per cent. The official British statistics published shortly after the war give an even higher margin of 50 per cent, as do the figures in a number of modern textbooks.52 In other words, the Central Powers were at least a third better at mass slaughter." pg 294

"The trouble was - and here the excuses must stop - that the entire culture of the British regular army militated against effective improvisation. The command structure was based on obedience to superiors and suspicion of subordinates; men could still advance according to their connections; and commanders could still be 'unstuck' by personal quarrels.83 This could have serious repercussions: when Haig questioned
Rawlinson's original Somme plan, the latter felt unable to stand his ground, with the result that Haig was able to insist on the suicidal breakthrough objective. As Rawlinson said, 'It is a gamble to go for an unlimited offensive but D. H. wants it and I am prepared to undertake anything within reason [sic].'84 An Army Commander did not presume
to correct the Commander-in-Chief, even when tens of thousands of men's lives were at stake.85 Similar inhibitions existed at every level. Orders were issued at the top and fed down the line; there was little traffic in the other direction. As a result, officers, NCOs and men grew accustomed to 'waiting for orders'. In battle, as J. M. Bourne has remarked, 'when German shelling interrupted communications paralysis set in'. To adapt the not inappropriate language of industrial organization, this was 'line management', and it provided no mechanism by which the views of 'junior line managers' could be relayed back to head office.86 Partly for this reason, the proponents of a more technocratic approach made slow headway against the traditional believers in war as a moral rather than material contest.87 Too much emphasis was placed on morale, courage and discipline; not enough on fire-power and tactics."
pg 305

"These German tactical strengths were rooted in a distinctive military culture. According to Dupuy, the German military establishment had 'discovered the secret of institutionalizing military excellence'.109 Martin
Samuels likewise points to a distinctively German philosophy of combat, which acknowledged its fundamentally chaotic character.'10 This in turn influenced the way command structures evolved. The Germans favoured 'directive command' (task-oriented and decentralized decision making, flexible at all levels) whereas the British preferred 'restrictive
control', which deliberately discouraged initiative."1 Differences in training also followed logically from this. German 'chaos theory' demanded a high level of training to promote adaptability; the British approach required only obedience. Moreover, the German officer did not stop learning on obtaining his commission; the officer corps was
meritocratic, and dud officers were ruthlessly weeded out."2 This line of argument has been further developed by the work of Gudmundsson on stormtroop tactics, which (he argues) depended for their success on the existence of a 'self-educating officer corps'."3 pg 309

If that's not enough, there's plenty more backup in the book. It's a good read, I recommend it.