So I actually set up my account on this forum to ask this question.
The question boils down to what a 'Star' actually entails, and how the Sundering may have affected it.
Midgardsomr and the Greatwyrms he sired are such terrible and powerful beings that have influenced the world since they arrived from a distant Star. They are an explicitly alien form of life, granted sanctuary by Hydealyn.
The reveal of the Sundering and how all people of the planet used to be capable of powerful creation magic also established that as a person's soul is rejoined with its shards, it grows denser and more powerful. An unsundered soul such as Emet Selch has near unrivaled power one-on-one, and appropriately need the co-operation of many weaker souls to do battle with.
So... is that part of the secret of the dragon's might? Did Hydaelyn only sunder *the planet itself* into the Source and the 13 reflections, and Midgardsomr's power is in part due to his arrival from an unsundered Star? This could well apply to Omega too, having arrived from the same planet. Their souls could be at their true 'density' and might, and it's only now that multiple rejoinings have occured that humanity can actually hold against them without outside assistance.
Altenrativly, the Sundering could have shattered the entire universe and there's a version of Midgardsomr's planet out there. There's little evidence the dragons made their pilgramage to the first, aside from I think one dragon enemy type which seems unique to the first.
Personally, I think the Sundering was localized onto just the Star of Hydaelyn and shunted the reflections into alternate timelines/dimensions, saving the world from destruction but unwittingly leaving it vunerable to invasion?
Does this also imply that a planet weilding that much raw power is doomed to destroy itself? I'm going to be closely watching for the truth of the Final Days in the future, that's for certain.