This reasoning shouldn't be following through with nearly every Splatfest if team size was not the issue. It's noticeable in maybe every Splatfest, with possibly 1 ever (if even) being the exception.

Even if somebody else plays Bobby's 15 games, that person will also play 15 games less than Drew. Drew will play 15 games less than Robert. So on. The fact that the counted win percentage average by each member adds up to a lesser win percentage than the lesser players should be true. I'm not saying each individual player will have my static example, but the group as a whole will need to miraculously have greater win percentages than their enemy in order to win. Otherwise, their win percentages remaining equal would mean that the smaller group always wins, because again:

Lets pretend there's Person 1, 2, 3, 4 for Team A, and person 5, 6, 7, 8 for Team B.

Team A has more players than Team B. Every player here has played 100 games, but Team A players have each played 30 games against each other.

This means Team A has played 280 games against Team B's 400 games. All have 50% win rates, so that's 140 wins for Team A and 200 for Team B.

Say that the 120 other games Team B played were against other players from Team A. Team A NEEDS to win at least 60 of those games or they lose that set.

This spans throughout tens of thousands of players with that requirement. Through statistics, the probability of getting the same statistic repeatedly after one another is nearly impossible. Somewhere down the line, the team with more players (that MUST put in more effort), will screw up, even if only by 1%. The effect dramatizes when there's so many players and games to consider.