In truth, as anybody who has been following baseball for more than two weeks knows, the best team does not always win. The 1960 Pittsburgh Pirates, my favorite example, had no business being on the same field as the 1960 New York Yankees. They won the World Series. The best teams the Brooklyn Dodgers ever fielded were their 1952 and 1953 entries. Both teams lost to inferior Yankee teams. By 1955, the Dodgers were aging and infirm, while Mickey Mantle, Whitey Ford were entering the prime of their careers. They were beaten by the aging Dodgers.
Luck plays a significant factor as well. Bill James created something he called the Pythagorean Record. Basically, a team's record, 90% of the time, will come within 10-15 percentage points of their Runs Allowed vs. Runs Scored differential. If you look at the current standings, there are 5 teams within the range of +14 and +17. Their records range from the Yankees 15-9 to the A's 13-12. When records vary, luck plays a significant role. The Yankees are +2 games in the standings vs. expected, the As -1. Usually, but not in all cases, things balance by the season's. Last year's Orioles, for example, finished the season with 12 more wins then their run differential suggested, due almost exclusively to what one would think of as an unsustainable record in 1-run and extra inning games.
While it's possible that the Yankees run of good luck will continue, it's more than likely that it will balance out. While they've had good pitching, they've shown considerable difficulty scoring runs when facing even average pitching.
There are, of course, factors that no one can measure at this point. The first is injuries down the road. The age of the Yankee team puts them at significant risk. The other factor is mid-season additions. Who will bail and deal off their expiring contracts and who will teams add as the deadline approaches. The Red Sox appear to need nothing at all, with five starters pitching well, the offense clicking on all cylinders, and the shut down bullpen. Naturally, they can't sustain a .720 record and will likely need additions. Their farm system is loaded, so help, most significantly Allen Webster, is at hand, but they also have considerable depth from which to deal.
Theo Epstein once said the season is divided in three parts. In part one, you assess your needs. In part two, you make adjustments to your roster, in part three you hopefully have a team that will get you to the playoffs.