It would've been nice to steal Jordan Montgomery away from the rival Rangers
The Rangers made one of the two major blockbuster moves with their Max Scherzer acquisition, but they also added Jordan Montgomery to an already solid rotation. Montgomery has been one of the best left-handers in baseball since being traded to the Cardinals last trade deadline and would've been a nice fit on the Angels.
Now, did the Angels really need another starter after they had already acquired Lucas Giolito? Not necessarily. However, it sure would've been nice to have him knowing that Griffin Canning would land on the IL on the day of the deadline. Chase Silseth has been good, but can't go deep into games and hasn't been reliable throughout his MLB opportunities.
Montgomery on the other hand, is Mr. Reliable himself. He has a 3.42 ERA in 21 starts and 121 innings pitched. He's allowed three runs or fewer in 17 of the 21 starts. He's gone at least six innings 13 times, and at least five innings 18 times. The Angels lack the consistency Montgomery provides.
I would shy away from saying Montgomery has the ceiling Lucas Giolito has, but his floor is also higher as we saw from Giolito's blow-up in Atlanta. The cost to get Montgomery was significantly cheaper than the cost to acquire Giolito even though they're both rentals. The Angels could've had both, and would've even been justified choosing Montgomery over Giolito. The fact that they have to watch him pitch for their division rival makes it hard to swallow.