After the
HH, I think Macharius has a good shout at it, as an effective human baseline leader that brought back a huge chunk of territory. Or maybe Slaydo, who had a similar experience.
I haven't kept up with the never ending gap-filling of Horus Heresy Street, but I'm sure there are quite a few similar types in there. The primarchs take most of the glory I guess, but I don't rate their exploits as much due to their massive mary-sueness. There must be some more baseline types in there as well that get the job done through reasonable competence, rather than heroic happenstance.
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Drusus seems tohave done quite well for himself, with 17m troops and the clearance of a sector.
https://wh40k.lexicanum.com/wiki/Angevin_Crusade