Consider the following, the Lion and Horus were considered the greatest tactical minds of the Great Crusade, but they also had the might of the Great Crusade Imperium behind them. That means Space Marine Legions of hundreds of thousands, a united Imperial Army(which includes a combined Navy/Guard), and a far greater tech level,
The power at their disposal shouldn't matter in a debate about tactics and strategy.
Also as you see aftet his death those world fell to instability but during the great crusade they were not only conquering but expanding the empire, building and expanding the new infrastructure.
This is also a really good point. The Primarchs built an empire of millions of worlds, Macharius didn't actually achieve anything of lasting significance. Surely that must speak to his strategic ability to pacify conquered worlds.
"Look into my eyes, and see your death."
"Let them hate, so long as they fear."