Is this the year of the Arizona Diamondbacks in the NL West?

For the last five years, the Los Angeles Dodgers have been the team to beat in the NL West. They’ve won the division the previous five seasons, and in that time, have won at least 91 games a season. Last year they won 100+ games for the seven-time in franchise history and for the third time since they changed coasts and became the Los Angeles Dodgers.
But while the season is still young, it appears that the Dodgers are no longer the team to beat in the NL West. With 46 games under their collective belt, the Dodgers are 20-26 and five games out of first place—which happens to belong to the Arizona Diamondbacks.
Last season, the Diamondbacks ended up surprising MLB fans everywhere by winning 93 games and earning one of the NL wild-card spots. They took down a division foe, the Colorado Rockies, in the wild-card game and earned a spot in the NLDS against another division foe, the Dodgers.

They ended up getting swept by the Dodgers, but there was a reason for hope. With a top ten offense and a top five pitching staff in 2017, if they could keep from taking a step back, they stood to be just as competitive in 2018.
The 2018 Roster
While they didn’t need to do anything to their roster, change is inevitable and part of every team’s offseason in professional sports.
The most significant loss was slugger J.D. Martinez. They had acquired him via trade during the season. While he was only with the team for 62 regular season games, he made enough of an impact to receive vote(s) for NL MVP (he finished 14^th after hitting .302/.366/.741 with 29 home runs).
Other notable losses included closer Fernando Rodney, infielder Brandon Drury, and catcher Chris Iannetta.
They filled the holes as best they could without spending a fortune. While they didn’t come close to filling the void Martinez’s departure left, they added some good players. Alex Avilla was a good addition at catcher and for the lineup. The team also had high hopes for Jarrod Dyson (acquired via free agency) and Steve Souza Jr. (via trade).

With Rodney gone, they would need someone to fill the closer role. As the season began, closer duties were going to fall to either Brad Boxberger (acquired via trade), Yoshihisa Hirano (via free agency from Japan), or Archie Bradley— or some combination of the three.
So far—eh, good enough
As of their May 20 loss to the New York Mets (their fourth consecutive loss) they are 25-21. They have a half-game lead on the Colorado Rockies and a two-game lead on the San Francisco Giants. The Dodgers have struggled all season and sit five games back and just a game out of last place.
While being in first is good news, it is largely because of the great start they had to the season. Through April, they had a 20-8 record and were playing pretty good baseball overall. They were not batting well (.232 team batting average), but they were pitching well enough to make up for the lack of run support (2.88 ERA).

The formula was working at the start of the season but was not a good one for sustained success. Sure enough, injuries started to take a toll on the pitching staff (3.33 ERA through May 21). The offense has failed to wake up (.219 team batting average through May 20), and they’ve been losing games.
Are they the team to beat?
For Arizona to be considered the team to beat, the offense is going to need to wake up. They will also need the pitching staff to get healthy and get back to dominating the competition. Technically, as the division leaders, they are the team to beat in the NL West.
But calling them ‘the team to beat’ makes it sound like they are dominating the division. What the Dodgers did last season qualified as a dominant performance. That is far from the case.
Arizona is not the team to beat in the NL West. Until they develop an offense, they will just be the team that happens to be in first. Should they start hitting, well—that could change.