To keep players motivated after their first match is over, it is awfully important there is something they can build up over time - something that remains after the current match. If you each time start from 0 after a match is finished, that's very demotivating. You need something you can look back to, something you can be proud of, something you can show to your friends. This something is your player profile. Therefore it is very important the stats and achievements show how good a player is. Which they currently - as you correctly said - do in a very imprecise and blurry way. The part of my proposal that's about the historic world map is one step to improve that.
Another step has already been taken by this update, because now maps fill up more reliably. So now it's more difficult to join a map with the hope it doesn't fill completely (and to win more easily, because less players means less competition). My proposal of more "starts when full" maps would even completely remove this nasty option - then there would be the same degree of competition in each game of the respective scenario.
People's appetite to collect something precious is a very strong incitement. What do you want to collect in CoW?
Ranking points? That's utterly boring, even the last dumbass gets many ranking points over time just by playing a lot.
Blueprints? No, that's a side-aspect of the game. Playing just to collect blueprints? No.
I tell you collecting victories would be THE THING. And for that it's mandatory you cannot tweak your chance to win by being the first on the map, by joining a game that won't fill up completely, or where you can grab the privilege to pick the mightiest nation from a historic map. That's why I'm suggesting more "starts when full" maps. That would not only allow the variety of scenarios to be widened again, but also make a victory meaningful.
I, and I imagine a lot of other players, play to have fun. I think it's would be better of Bytro to keep their old customers happy by keeping a fun game (where I can choose my country and have minimal inactivity) than try to draw in new people who only care about the game because they want to collect the shinys. It doesn't matter to me how many new players join if none of them remain active becasue they got the wrong country.