Just a quick-and-dirty assessment.
Over the last three seasons, Joe Saunders has averaged (via FIP) ~0.06 wins above replacement per start. This year it’s dropped to about 0.05.
Dan Haren has so far put up a WAR of 2.6. That’s a down year for him after back-to-back years of 6+, but it’s still good. Over the past three seasons, that’s about 0.17 wins per start. A move to the AL probably drops that to about 0.14.
Saunders was probably good for about 12 more starts going forward. While he’s not good and Haren is very good, over those 12 starts at these rates, that’s still a difference of only ~1 win. Even if Haren completely regresses to his previous greatness and somehow suffers no loss moving to the AL, that’s still not even quite two wins.
In short, the Angels are now better, no doubt, but this isn’t a race changer. Before this trade, you would have to expect the Angels to be at least six wins better than the Rangers going forward to think of Haren as a threat. The race is a little less comfortable now, but only a little.
What’s frustrating is not that the Angels have now closed the gap with this trade. It’s not even that they’ve necessarily made themselves better than the Rangers the next two seasons. It’s that making deadline moves is supposed to be painful. It’s supposed to mean going all-in on a rental and losing a chunk of your future in the process. Instead, the Angels got better this season and for the next two seasons (at least), and didn’t have to give up much to do it. And it’s further frustrating that the Rangers finances aren’t in a place that they could do something like that.
The Angels aren’t suddenly much scarier than they were yesterday, it just sucks their distant future didn’t get much less scary in the process.