I tend to believe that odd numbers make it more interesting. Four player games tend towards one side retreating after either the loss of an aircraft or severe damage. With the addition of another player the games run longer as the loss of a player either evens the fight or makes it a running fight to escape. Much more fun.
Experience of the players involved is also a huge factor. 2 vs 3 could turn out to be unfair for the team with 3 if you have all veteran players on the smaller side!
In the late 90s, Jim Pink brought his 8 yr old son JJ to the Spring Mini Con. We had 5 players and JJ and I ended up as wingmen. Jim was worried that I wouldn’t have fun flying with an 8 yr old and suggested a change. I had seen JJ fly earlier at the Con and Jim had done a superb job of teaching JJ the basics of the game. And I didn’t want JJ to feel bad so I said no , we’d be fine.
Long story short, we shot down 2 and Jim was the last opponent who moved away from combat on the last turn ,where upon JJ says, “Run like the dog you are Dad!”
A fond memory and a pefect example of why I still play this game after 30 some years. Anything can happen regardless of even numbers or not.