The power at their disposal shouldn't matter in a debate about tactics and strategy.
And there are hardly any details on those tactics and what strategies they used, so the resources they had at their disposal and the end result is all we really have.
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.
That wasn't his job. His job was to conquer, it was the "missionaries and Inquisitorial teams that followed those conquests that were supposed to do the job of turning those planets into loyal parts of the imperium.
Same for the Primarchs, they conquered, but for the most part it was the Imperial Army and the Orators who's job it was to maintain those conquests.