While relatively minor in terms of WAR, it's a very interesting trade to analyze.
There are a couple other factors worth considering:
1. The Twins traded Pressly in 2018, but then turned around and traded minor league assets for relief help at the 2019 deadline. Had they kept Pressly, maybe those assets could have gone toward bolstering the lineup and rotation instead. Hard to imagine what would break the playoff curse at this point, but a different approach in 2019 (and 2020) could have helped.
2. Alcala and Celestino could easily out-produce Pressly over the span of their team control years -- but if those performances come in seasons when the rest of the team is poor, they may be less valuable than Pressly's 2019 could have been to a postseason team.
3. I'm not sure how to phrase it, but piggybacking on #2, I think future WAR can often be "discounted" a little bit compared to present WAR. Maybe "opportunity cost"? If Alcala contributes 1 WAR to the 2022 pen, that's nice -- but it's not as if we would have been 1 WAR worse in 2022 if we hadn't made the Pressly trade. Four years of FA, trade, and development decisions would have all changed a bit in that alternate scenario, and we probably could have come up with a 2022 alternative that provided some percentage of Alcala's contribution. Enough that a slight edge in WAR may not be enough to tip the scales toward the Twins side of the ledger -- some plus performances from Alcala and Celestino might be necessary for that.