In many ways, the Cubs have been the best team in the National League in 2018. Maybe that will surprise you. Maybe it should. Other than a brief two-day stint at the end of April, they haven't been in first place all season. They were in fourth place as recently as May 26. If you're a fan of the Brewers or Braves, who each have more wins, you're probably in shock. How could a team with fewer wins be the best in the league?
If this were the end of the season, that'd be correct. Wins and getting to the playoffs are all that matter over 162 games. But in the first week of June, with nearly two-thirds of the season left, current wins aren't the best way to predict future wins. (Just ask the Twins and Rockies, who were in first on June 6, 2017.) Underlying skills are -- and the Cubs have shown pretty much everything you want in terms of expecting great things ahead.
Let's oversimplify. Let's reduce baseball to the four fundamental skills -- pitching, hitting, baserunning and fielding -- along with run differential, which has a very strong relationship to winning percentage. Take a look at where the Cubs rank in each. You can probably guess it's "very good" in all of them.
Pitching
The Cubs have the second-lowest ERA in the league, 3.22, behind the Nationals, and third in the Majors behind only Washington and Houston, and the Cubs have allowed the fourth-fewest runs per game overall (3.61). That includes the ninth-best rotation ERA (3.67) and the second-best bullpen ERA (2.58). They've done this in part due to a 47.7 percent ground-ball rate, the best in baseball. Grounders don't turn into homers; only two teams have allowed fewer.
Hitting
They have the best park-adjusted offense in the NL, third in the Majors behind the Yankees and the Red Sox. (That's a 110 wRC+, for the statistically-inclined among you, or 5.15 runs/game for the traditionalists. Each is best in the NL and third in MLB.)
Baserunning
The Cubs have just 24 steals, tied for 21st in the big leagues, but there's more to baserunning than steals -- like the fact that the Cubs are tied for the third-highest percentage of extra bases taken on the bases. Using an advanced baserunning metric like the one that FanGraphs provides, which accounts for things like the fact that only one team has grounded into fewer double plays, the Cubs are baseball's best baserunning team.

Fielding
Since we haven't yet included infield play in Statcast™ metrics, let's go with the usual advanced stats. The Cubs are third in Defensive Runs Saved (+32), they're first in the NL (and second in the Majors) in Ultimate Zone Rating (16.6) and they're first in FanGraphs' all-inclusive "Defense" metric, which gives more credit to a slick-fielding shortstop than, say, a good first baseman.
Run differential
With 294 runs scored and 206 allowed, the Cubs have a +88 run differential -- the best in the NL, and third only to Houston's +122 and Boston's +96.

Up and down the line, the Cubs stand out.
If you like depth, the Cubs have that, too. If you prefer to think about it in terms of "most useful hitters," the Cubs' offense features nine batters who have at least 100 plate appearances and at least a 90 OPS+, which is tied for the second most in baseball. If you prefer flipping it upside down and viewing it in terms of "no black holes," the Cubs are one of only four teams in the game with one or few players to have at least 100 plate appearances with an OPS+ below 90. (None of this includes pinch-hitting ace Thomas La Stella, who has hit .329/.405/.357, but in only 79 times up.)
It's the same story on the pitching side. The Cubs have 14 pitchers who have thrown at least 10 innings and have an ERA+ of at least 90, the most in baseball. They have just a single pitcher, Yu Darvish, who has thrown at least 10 innings with a performance worse than that. No other team can say that. The Marlins have 13 such pitchers.
This is all following a 2017 where a resurgent Cubs offense scored the most runs in the game in the second half (423). It's a season where Kristopher Bryant has legitimately been one of baseball's best hitters, where Benjamin Zobrist has rebounded well from a down 2017, where Kyle Schwarber, Javier Baez and Albert Almora Jr. are all having what look like career years, where Ian Happ and Anthony Rizzo have rebounded from miserable Aprils (.196/.277/.294 between them) to look like stars again, where even Jason Heyward, hitting .333/.364/.451 since his May 18 return from injury, is showing signs of life.

So this is a good, talented, deep Cubs team. Why doesn't it feel that way?
It's primarily because of the standings, of course. Since they've spent the season largely bouncing between second and fourth place, it feels as though the Cubs have underachieved, and to some extent they have. (Based on expected winning percentage indicated by that large winning differential, the Cubs may have played like a 37-20 team, not a 33-24 club.) That has a lot to do with how tough the NL Central has been and how well Milwaukee has played, even though the Cubs have taken seven of eight against the Brewers.
It's also about some of the struggles of a few high-profile pitching imports. While Jonathan Lester (2.44 ERA) and Kyle Hendricks (3.59) have been mostly excellent, last year's big trade acquisition, Jose Quintana, has been inconsistent (4.30), free-agent add Tyler Chatwood (4.02) has more walks than strikeouts, and Darvish (4.95, currently injured) has hardly lived up to his reputation as Jacob Arrieta's replacement.
There's also this: The Cubs haven't exactly been clutch, however you define that word. They're hitting just .216 in 'high leverage' situations, the sixth-lowest mark in baseball. That's part of why they're just 5-10 in one-run games, baseball's sixth-weakest record. That's despite the fact that the bullpen has generally been excellent -- free-agent acquisitions Brandon Morrow and Steve Cishek have combined for a 1.36 ERA and 50 strikeouts in 46 1/3 innings. According to the most advanced Statcast™ quality of contact metric, this is tied for the third-best bullpen in the NL.
The good news is that "clutch" isn't really a skill. It can easily come and go -- and even with those concerns, the Cubs still have that lofty runs per game mark. For all of Darvish's issues, he's still striking out hitters at the same rate (27 percent) as he did last year. If they decided to go out and replace the relatively disappointing Addison Russell with Manny Machado, well, they could certainly go ahead and do that.
While the Brewers surely can't be overlooked at this point, there's a reason that the Cubs are projected to be tied for the third-most wins in baseball from this point forward. At the end of the season, it may be true that "you are what your record says you are," to paraphrase a famous saying. It's the first week of June. The Cubs' record says they're pretty good. Their underlying numbers say they might be great.