Iglesias is a guy who was available to the whole league before 2020 and signed for 1/$3M with a club option. For 2019 he signed a minor league contract (made $2.5M in the majors). Those give us some indication of his value around the league, and it's not very high. Those aren't the type of guys that get you much of anything if you're trading them. Maybe a back of top 30 guy? Well Stallings is 26th per fangraphs.
Could his value have gone up due to 2020? Maybe, it was the best hitting "year" of his career. But it was also only 150 PAs, with a BABIP .100 above his career average. And he was hurt most of the time. I doubt 2020 moved the needle much, I would think most teams would see it as an obvious outlier and expect 2021 to be closer to his normal levels (which has happened). His normal levels that are valued by the league at around 1/$3M.
Everything you said is true, but IMO there is one more thing to consider, and that is, is the return for the player you are trading as much or more than he is worth to you? My issue with at least some of Elias's trades, is the answer to me is no. The real value in some of these trades seems to be cutting the payroll. I think the value of the Iglesias deal on the face of it seems to be, that they were able to free up money.
Now if Pinto or Stallings turns out to be a key piece, than Elias wins the deal