I think there may be three discussions going on here:
1. What is historical?
2. What will create a historical outcome in SP?
3. What will create a historical outcome in MP?
The first two questions may have different answers. Perhaps it is historical for Sweden to have Ugric. But if having Ugric culture makes Swedish AI conquer Norway, Denmark, or Novorogod with ease; then perhaps you need to do something that isnt quite historic to get a historic OUTCOME; which is different.
I have always been in favor of bending the TRUTH to create a historical OUTCOME. These are different things. First, we need to come up with a theory to explain Sweden's rise to power. If it is economic, then we need to provide some economic changes for Sweden. If it is military (probably imho) then we need to provide some military changes for Sweden. But we should use history as a guide, not a straight jacket.
If we are concerned with geographic outcomes, we just need to change certain variables to create the outcomes we want. Lets divide Swedish history into two pieces; early and late.
During the early period, we want Sweden to be able to defend herself, but not really expand into Norway, Denmark, Germany, or Russia. So we could lower her wealth and manpower during this period but increase fortifications and lower support limits in all of Scandinavia (they are far too high for such horrific terrain). This way, Sweden AND Norway will be hard to conquer (historical) but Sweden will be unable to project power outside of her country (also historical).
During the late period, we want Sweden to be able to conquer certain regions on the Baltic Coast and some parts of Germany. During this period, we should raise her economic and manpower values, boost her tech, and provide her with lots of free soldiers. You could even tweak DP sliders a good bit to generate morale advantages. The leaders during this period should be very good and Sweden should be given extra transports and galleys. She should have local fleet supremacy against minors; but not against Denmark (hence the galleys/transports) This way, Norway and Sweden will still be hard to conquer (historical), but Sweden will be able to project her power outside of her country (also historical).
The early period changes could be made directly to scenarios. The late period changes would have to involve event alteration as well.
Despite the innocent pleadings of many Sweden lovers (Johan included), Sweden is way overpowered and Denmark is underpowered during the early period. During the late period, there is room for debate. Unfortunately, by this time AI Sweden's neighbors are AI Poland/Austria/Netherlands. Not good.
Despite the subject of the above changes being SP AI Sweden, I think these edits would transfer nicely into the MP world. Though I do think that having 10 uber-leaders is a bit much for an extremely short-lived stunt as a world power.