Victoria 3 will be, first and foremost, a GAME, rather than a SIMULATION. It will be tied a bit loosely to history in some places, tighter in others, but ultimately the limitations of computer hardware (now, not 20 years from now), programming time and cost, and the ability to present information to the player in a form that's easily understood and acted upon, will determine how "realistic" the game can be without chasing away customers or failing to recover its development costs and earn a healthy profit.
The bottom line is, if that's totally inadequate for your purposes, then you may need to start your own game company, fund it with a nearly unlimited supply of cash, and then be prepared for it to earn back far less than it cost to produce your masterpiece.
I don't expect anywhere near "perfection", but I'd like to see some economic and political game mechanics which at least resemble reality enough to produce relatively believable outcomes, rather than blatantly absurd antics by either the player, the AI, or both. The changing nature of warfare over the time span, and the design decisions made in that respect, means that the military system(s) will probably cover part of the period well enough, and other parts poorly, but I can probably live with that if the rest is good.
As for "the best game ever made", there are people who prefer FPS games, those who play RPGs, those who play strategy or "grand strategy" games. Victoria 3 may well become the best economic game of the bunch, and the Victoria IP is already the best "historical" Paradox game of the 19th Century, for lack of competition if nothing else. I wouldn't call it "the best game Paradox ever made" for most people, however. There are a whole lot of customers who prefer games like City Skylines or Stellaris. Personally, I consider it and HOI3 two of the "best" Paradox games for totally different reasons, and am glad that such diversity exists.
