It will be your defending champion New York Yankees facing the team of the teens, the Boston Rustlers, in the Alt-1921 World Series. For all the angst that gripped the Yankees fanbase and the sensationalism of the sports press, the Yankees won 55 of their last 81 games and ended up winning the pennant by a substantial margin. The surprising Athletics did finish in 2nd, 9 games back, with the Red Sox limping home in 3rd. I'm not intending to make this a 1921 recap post, so I won't dwell on this stuff now.
The Rustlers' road to the pennant was somewhat less inevitable feeling--they played well in every month but May (when they went 14-13), and while they were at a "mere" 50-31 in their last 81 games, they needed a terrible (11-15) September from Brooklyn to take command of the race. They did steadily build their lead over the last few weeks, and ended up 4 games ahead of the Robins.
This Rustlers team has very few of the key contributors from the 1914-1916 dynasty--only Rabbit Maranville remains from the 1914 OG Miracle team, and he seems to be entering his post-prime years (his OPS+ was the worst since he became a regular in 1913). Tillie Walker was one of the main hitting stars for the largely punchless 1916 champions, and he remains their RBI leader and cleanup hitter at age 34. The Rustlers have always been built on their pitching, though, and the most important holdover is Art Nehf. Nehf won the 1917 and 1920 Cy Young Awards, and again led the NL in ERA this year. Importantly, as we'll get to shortly, he's also a lefty. Nehf was traded to the Giants in 1920 in real life, but here he remains in Boston.
As noted, the Rustlers are built on pitching. They led the NL in ERA (overall, starters' and bullpen), had the fewest runs allowed (as you'd expect), the fewest walks, lowest opponents' batting average, and also had the highest defensive efficiency and zone rating. What they didn't do was strike people out--they finished dead last in the NL in that category. What they also can't particularly do is hit--they were 9th in the NL in OBP, 7th in SLG (and so, 8th in OPS). They're 3rd in WAR, but I think that's heavily inflated by their defensive work. They're 8th in runs scored, last in walks, tied for 8th in home runs. They're also 8th in stolen bases, perhaps because they don't get on base very much?
The pinstripes are, by comparison, not only much more capable with the bat but also more balanced. They led the AL in every important batting category save walks (2nd), baserunning (2nd), and stolen bases (last). They also struck out more than any other team, but I'll take that. Pitching-wise the Yanks were middle of the pack. They were 5th in ERA and starters' ERA, 3rd in bullpen ERA. They were great at preventing walks, but also didn't strike out many people. They were again mid-pack in defense.
The Yankees are a _very_ left-handed team, and the usual/best lineup has 6 lefties out of the 8 position players. The bench is a bit more balanced, with Moore and Rogan providing some right-handed pinch-hitting possibilities, but Terry, Pipp, and Goslin would probably be starting players on any other team in the majors rather than serving as left-handed pinch-hitters and defensive subs. In any case, the Yankees struggled, relatively speaking, against lefties with only a .564 winning percentage (.666 vs. righties). Interestingly, MLB as a whole only won at a .465 pace vs. lefties compared to .509 vs. righties. The reason this is important is twofold--the Rustlers' only lefty is Nehf (though maybe they'd be liberal with using him in relief), and this would seem to be a big advantage to the Yankees' big bats. Second, they only have one lefty in their lineup (Alejandro Oms, who might also be their best hitter). This might keep some of the Yankees' left-handed relievers from seeing much action in the series, but there really aren't many of them--since Pennock is hurt, it's really only Mogridge and Robinson. So, the Yankees can potentially be looking to use Hendrix, Rogan, Caldwell, etc. to get and be able to keep the platoon advantage in big situations. The Rustlers hit well against lefties (.300, with a better than league average OPS!), so having them not face lefties unless strictly necessary seems like a fine plan (even if Eppa Rixey might not approve).
As far as individual players--in past Yankees-Cardinals matchups I'd noted that Rogers Hornsby was probably the best player on the field, maybe followed by a few Yankees. Here, it just plain looks like the Yankees dominate the discussion. Batting-wise, there is no question--the top 7 non-pitchers by WAR are all Yankees, in other words every member of the entire Yankees starting lineup (save Peckinpaugh!) has a higher WAR than any member of the Rustlers' starting lineup. After the top 4 Rustlers by WAR comes Charlie Blackwell, then two more Rustlers (including their backup catcher), then Peckinpaugh and two more Yankees' bench/backup players (Rogan and Moore). Twelve players on the two teams had 500+ plate appearances, the 7 Yankees on the list all had higher OPS+ than any of the Rustlers.
Turning to the pitchers is admittedly murkier. The relationship between pitching WAR and pitching success in OOTP is a bit hard to get my head around, but the top two in that category are Yankees (Rixey and Faber), and while Donahue of the Rustlers is in third he's also injured and out for the season. The next four players on the list are all from Boston. The ERA+ situation for qualifying pitchers favors Boston more, but isn't quite as lopsided as the OPS+ situation.
OK, so. Prediction. I've seen a lot of things go not-at-all how I'd expect. This is a great Yankees team, if not quite as good as last year's. I've seen this team simply unable to beat bad teams, and shut out unexpectedly. But I feel like the Rustlers will need another miracle. I'll spot them two games that Art Nehf wins, but I think that may be giving them too much credit. Nevertheless, Yankees in 6.
EDIT: I realized something I should do is look at the park factors. Allston Grounds, the Rustlers' home park,
severely depresses offense. The Polo Grounds
severely increases home runs. NL teams slashed at .281/.333/.389/.722 on the road, and Boston did better than average at .293/.340/.403/.743. AL teams on the road hit .284/.336/.400/.736, with the Yankees at a tremendous .309/.363/.453/.815. Pitching-wise, AL road teams had an OPS of .761 and an ERA of 4.23, the Yankees kept opponents to an OPS of. 733 and an ERA of 4.03. For the NL, the matching numbers are .754 and 4.08, with the Rustlers pitching at .729 and 3.60. The road batting OPS for the teams ranks 3rd (!) for Boston and 1st for New York in their leagues, the road pitching OPS ranks 4th for Boston and 3rd for the Yankees. For individuals, Charleston drops down to be pretty average on the road but 6 of the top 7 qualifiers remain Yankees when ranked by OPS+, while only three qualifying pitchers have road ERA+ higher than 100 (Nehf, Schmutz, and Hendrix). Meanwhile, Luque and Barnes have been great on the road, while Blackwell and to some extent Moore also struggled there.