Let's see what the verdict, outside Arizona fandom, is for the deal
The general opinion appears to be less that it's a good or bad trade for the Diamondbacks, and more that it isn't a very good one for the Mariners, because it doesn't address their problem. For example, according to David Schoenfield of ESPN, "The problem is they don't have hitters, they don't have enough guys who can get on base, they haven't developed hitting prospects... Trumbo is hitting .259 with a .299 on-base percentage. He has a career .298 on-base percentage.