Too many players and the victory is impossible, actually. Since the target vote increases per player (the amount it increases with depends on the class of course) and there's a set amount of votes available in the world, you can create some huge coalition if you want, but it still wouldn't be enough if the entire world votes for you.
I don't really think 'drawing' with other players would be less of a victory in this case. For example, one B power would need X votes and 2 B powers would need 2X votes to win. Is either one easier? Very much depends on the situation. Maybe being in a coalition together and trying to win together is the only thing preventing them from shooting eachother to pieces, making it a powerful diplomatic tool, but this alliance COULD be betrayed if one ally deems it an easier way to win. The betrayal wouldn't even necessarily involve a nuke strike; if you have enough voting support, you just propose the 'coalition' with just you in it and take the win. You'd need enough voting support though.
In it's current state, the 2 B powers would likely just be wrapping up their certain victory while everyone else eagerly tries to get that third spot.
The methods for winning should improve gameplay, ideally. As I illustrated, this way, there's only one point when you can say with confidence you're going to win: when you've won. Everything can happen from start to end. As the game stands now, a lot of people already know they've lost come voting season.
By far the most important reason though, is that while Georgeatkins is right that all rules are arbitrary, the current coalition rule isn't just arbitrary, it creates arbitrary mindsets, arbitrary gameplay.
In Fire&Blood, we created Fight Club: a group of minors around the globe who simply looked for ways to help eachother out in secrecy, sharing extremely useful intel about to-be stabbers, amongst other things. No one else knew, but a bunch of us just kept growing larger.
Then I realised Fight Club couldn't win because a coalition is three countries, so I effectively went batshit crazy in an effort to get me in the winning coalition, because I knew that right now, I wasn't going to be in one.
I went all or nothing, and got nothing, because there was no other option: no possible 4way draw to get into, no reason for the coalition heading for the win to compete with eachother..
All because of the arbitrary number 3, Fight Club was bound to fail and my country effectively committed suicide.
The arbitrary number 3 does a lot with people's mindsets. People who play to win even when a win is impossible face almost certain doom, while those who choose to go for a survive instead cowardly wait for the game to end.
Not to mention what I said before: fixed alliances. You'd get rid of all of that and create a much more dynamic rather than static game if the arbitrary number 3 is removed.
I see your point but it is a different point. I'd like to ensure you know that when we speak of a coalition, we are not speaking an actual game alliance. In most cases, the two are different. Game alliances are what we use to help prosper and get to the end of the game. Coalitions are proposed towards the end of the game and can be proposed by anybody, composed of any group of 3 players. This is completely different from what you were talking about in your game. Your "coalition" is really a game alliance.
A coalition proposal is more like an end-game popularity contest, but can be based on any motivation, such as:
a. Revenge - a coalition is proposed to oppose a player that the proposer would like to see lose.
b. Respect - a coalition can be proposed to acknowledge various players for their efforts, even if they have nothing in common.
c. Politics - A player who proposes a coalition for which they are a member is going to canvas other players to gauge which players are most likely to get voted for. This player may propose several coalitions at the same time, in fact.
So, you sill want to make a coalition of any size? You'd have to figure out the revised votes necessary to win based on the coalition power sizes (A, B, C, etc.), which would be much more complicated and certainly much larger in total votes. If you start with 40 players, by the time we get to the end game, at least 1/3 to 1/2 of the players will usually have been eliminated. I believe at least half were eliminated in this game. That means a coalition of 10 players would constitute up to half of the 19 or 20 survivors. 6 players would be 30%. A coalition of 3 constitutes 15%, which makes more sense and has more significance. Is there any great value being in a coalition composed of at least 30% of the surviving players?