I think a major argument against Vicky is that it's impossible to accurately simulate the progression of the means of war over this time. For the same reason as there shouldn't be a game encompassing the entire 20th century. Both on land and at sea the technology progresses so much so quickly that it cannot be depicted in a satisfactory manner.
I disagree, I think they were on the right track with Vicky 2, the only issue as the direction they balanced it along.
In Vicky 2, you start with a system that is pretty good at simulating single concentrated point line battle technology of the Napoleonic era, and end with that same system but with some tweaks such as combat width that are meant to account for the shift to frontline based combat.
I think a much better system would be something that is instead anchored at the end, a frontline based system, but with tweaks for the start so that it can function adequately in the earliest decades when armies were better concentrated at single points. The frontline functionality would always be there, but the AI would simply not start spreading its forces out until it had exhausted the limits of combat efficiency from concentrating. This really only requires 2 major differences then in a potential Vicky 3:
1) Drop in the Hearts of Iron frontline system into the combat
2) Create an AI that knows to only spread forces out once a concerted push is no longer as efficient.
The first is simple and the second task in theory should already have been accomplished in HOIV. The AI in that game should be capable of stacking up its forces at a single point when that is necessary for a breakthrough, instead of spreading its forces over every province. In theory, you could instruct it to gauge whether additional forces increases chance of victory in a battle substantially, and if not, to simply split off forces and move them on the flank. Once armies are big enough, this will happen repeatedly in a "Race to the Sea," resulting in frontlines of any size between Napoleonic, late Civil War, and WW1.
At sea it isn't much different. Make the game functions for a WW1 navy but leave most of them unused at first. Ships becoming obsolete is not the special circumstance of this period, and the AI can learn to keep wooden ships away from dreadnoughts in the same way it keeps convoys out of the way of battleships, uneven technology is a normal part of naval combat in the modern era. As for the particular naval tactics used, the games hardly reflect this level of detail to begin with, so it doesn't require much more than modifiers to reflect the earlier battle formations.