This is the part that I have trouble getting over. If they had signed a top starter and a RH bat first, while maxing out payroll, I could understand this move. At that point, you'd have done everything else you could and a trade would be necessary to complete the roster.
As things stand, their period of contention isn't today. It's probably in 2-3 years when Anthony, Mayer, and Campbell are hopefully settled in (similar to how the timing of contention worked with Bogaerts, Betts, Devers, & Benintendi). Unless they were concerned about Teel and Montgomery losing significant value in the next year, I don't understand the need to make a move like this today (besides panic and desperation because Plan A, Plan B, etc failed firs).