Something to keep in mind with the A's broadly is their new park this year has been the second most hitter friendly in the league after Coors. And park factors at places like Fangraphs aren't perfect at accounting for that (they use 3 or 5 year averages typically). Severino certainly hasn't been *good* by any stretch of the imagination, but I think in that ballpark average is probably an ERA north of 4.50. He's probably been roughly Colin Rea quality when you account for park and defense.
That said, unlike someone like Gallen or Alcantara who I really liked coming into the year, I wasn't high on Severino to start with. So even if getting him out of Sacramende turns him back to normal, I don't love his normal. And what I wrote above about park factors needs to color how you look at Urias. Ultimately while I'd do this trade in a vacuum, I suspect there are other overlapping deals I'd rather pull the trigger on, like a Keller/Bednar deal.