At this point, my main question is less about the ramifications of Argus having a world-soul, and more about the ramifications of world souls in general. So far we've got two worlds with confirmed world-souls where the species on that world have become unusually strong. The eredar were powerful enough to draw the personal attention of Sargeras, who, rather than simply wiping them off the face of Argus, offered them a chance to join him. The Legion's other races, stands to reason, got similar offers for being similarly-noteworthy.
And multiple times, the Legion has tried to sway the standout races of Azeroth to its cause and resorts to invasions when it fails. Now, the big difference is that most of the eredar took Sargeras up on his offer, while the races of Azeroth settled for kicking Archimonde's and KJ's teeth in. There's also the matter of the Well of Eternity being confirmed as a giant bleeding wound that reaches all the way down into Azeroth's world-soul.
Bear with me on this one, because I'm about to pull out a somewhat flawed analogy given the stark difference in individual power, but I can't help but feel like worlds with a world-soul effectively radiate out power to the races living on it, much like the yellow sun in DC continuity empowers Kryptonians. While the eredar benefited, greatly, from Argus's world-soul, that bleeding wound on Azeroth basically put the various races of Azeroth, native, alien, or evolved/cursed, on fast-track steroids--hence why we have done multiple times over what no other world has managed to do, why we're so special, even when we're technologically outclassed and dealing with millennia-old beings packed to the gills with magical prowess. I can't help but wonder if prolonged exposure to energies radiating from the Well of Eternity, worldwide, have caused us to grow in power to the point where we surpassed the eredar in a fraction of the time.