Chicago isn't exactly healthy either. The bullpen has been gutted by injuries to Phil Maton, Gavin Hollowell, Ben Brown, Hunter Harvey and Riley Martin, and Justin Steele and Cade Horton are both out for the rotation. Depth is the separator here, and right now the Cubs have more of it than Arizona does.
The Cubs arrive off a wild finish to their Seattle trip, dropping the first two games before exploding for 19 runs to close it out. That kind of offensive ceiling matters against a Diamondbacks pitching staff running on fumes. Arizona, for its part, has won its last game and took 2 of the first 3 in its set with the Reds, so this isn't a team in freefall — just one that's short-handed at the worst possible time.
Injuries are piling up on both sides of this one, though the flavor is different. Chicago's are mostly bullpen arms and complementary bats — Matt Shaw and Dansby Swanson among them — while Arizona is missing multiple guys who'd normally be starting games, plus Ketel Marte and Lourdes Gurriel Jr. out of the lineup. Losing a setup man stings. Losing a third of your rotation changes how a series gets played.
Chase Field's roof figures to stay shut with temperatures near 107 degrees outside, so the traditional summer-in-Phoenix scoring boost isn't really in play here — this one comes down to which pitching staff can hold up, and only one of these two teams has a full deck to work with.