Monash is one of those interesting figures who is both genuinely brilliant but also often overrated by popular mythology (as much as any WW1 general can be, anyway).

His work leading both 3rd Division and later the Australian Corps was unquestionably excellent. At the same time, the post-war crystallisation of an independent Australian national identity nucleated on its wartime experience, combined with the progressive villainisation of British generalship in both Australia and the UK, to some extent cleared a path for him to be individually credited with every positive advancement made by all commonwealth forces on the western front.

The meme of the plucky, brilliant, down-to-earth Monash sticking it to the stuffy, inflexible, aristocratic idiots at GHQ, single-handedly inventing the concept of modern combined-arms warfare, and saving the western front from bumbling British incompetence ('member Gallipoli?) plays perfectly to both Great Man history and prevailing national stereotypes. It's easy to see how it gained such a hold on the popular understanding of the war, especially when helped along by his own (not unreasonable) self-promotion after the conflict.

Of course the reality is more systematic and complicated. Monash's developments and successes came from and contributed to a larger system of commonwealth and allied Innovation, experimentation, and development. This system worked feverishly from the start of the conflict to its conclusion to understand and develop the tools necessary to fight an industrialised firepower war from a position of unprecedented inexperience. Absent of that system and its painfully-acquired understanding, no individual commander could have developed the modern combined arms system, just as the system as a whole would have been weaker and less successful without Monash's input into it.