The term "upset" is rarely used in baseball. the game is played in rotations. You can't bat Cody Bellinger every time or pitch Clayton Kershaw every time and you are a different team with a different batter at the plate or a different pitcher on the mounds. There used to be minimal physical contact between teams: now there is none. There is no blocking, tackling or checking into the boards. You can't physically force the other team to lose. Defense doesn't generate offense and offense can't make defense irrelevant. You get into the playoffs and how many regular season wins you had is irrelevant. We've had a World Series between two wild card teams.
That makes for an exciting post season but it also means that the best team is least likely to win in the sport that has the longest season, (they play twice as many games as basketball and hockey and ten times as many as football). It's also a summer sport that becomes much less appealing in cold weather. The World Series used to be in early October. then it was in mid October. Now it's in late October or November. The expanded playoffs have virtually eliminated true pennant races. the only race that matters down the stretch is the Wild Card race and that only heats up in the final week. August and September used to be about the baseball pennant races. Now they are about Hard Knocks and the beginning of the football season. people look at October baseball and say "Gee, are those guys still playing?"
That's why I liked the four divisional set-up more than the current six division set up with the wild card. Add two expansion teams and make it four 8 team divisions. Baseball had two 8 team leagues for 60 years and every team that made the World Series in those 60 years was at least 20 games over .500 and had the best record in their league. They played 7 game series which ended in warm weather. The best team almost always won. Baseball, with no or little broadcast revenue, survived a depression, two world wars and it's own apartheid. Fans of the also-rans didn't lose interest, at least not enough that they went out of business. And today they remain afloat from TV money anyway.
I remember a debate about this, (I think we were using the Connecticut board for baseball at the time), in 2005 about this and other posters were incredulous that I wouldn't want the Yankees and the Red Sox meeting in a post season series every year, just as they had in two classic series the previous two years. The league had set things up so those two teams would play a four game series to end the regular season in Fenway Park. Everybody looked forward to that. But they had both guaranteed themselves playoff positions before that series, which became Scranton vs. Pawtucket as a result. Everybody said, "So what? They'll be playing for the AL championship in a couple weeks anyway." The next time the Yankees and Red Sox met in the post season was last year- in a divisional series.