It actually doesn't assume anything other than the the need MAY be greater than it was a couple of days ago. This really has little to do with the fact that it's Steven Wright. A roster spot has opened, in a sense a decision has been made for the team and early accounts (yes it's still early) isn't showing a lot of promise out of a bullpen that went into ST with more than a few question marks. The catching core has limited value, but if Swihart seems to be the odd man out he may hold some value to someone in a utility role. Perhaps there is something else of value to another team in the Sox system that they can pair him up with to bring back a piece.
Funny thing is, I think the Wright news makes it more likely the Sox carry 3 catchers because now they do have the roster spot. As you said, no one hasn't shown much promise out of the bullpen, so why carry an extra arm? Especially in the early going. Maybe that's not the case this year, but usually in April you don't need your 5th starter for the first couple weeks.
I also think all of our catchers have 0 trade value but would all be easy to trade away for salary relief. Maybe you could get some 18 year old flier in the DSL for Swihart. I think at least one team would give him the chance to fail at catcher. If his splits are real and he is a fringe average bat vs RH, even if he doesn't stick at catcher, he probably has enough value to stick around as a Brock Holt type. He can arguably play every position outside of SS (and has) and can act as a pinch runner. I predicted him to be the next home grown Redsox prospect to be a much better base stealer (based off of trends) at the major league level and he's proven me right so far. The only prospect who has gotten
worse stealing bases is Mookie Betts (and Lin, but it's 72 games), but I think that's because he was the only one getting serious volume in the minors. I don't know if this is a player skill, team skill or combination of both. I'm guessing the latter.. Since Swihart is actually pretty fast, I could see his SB totals being significantly higher than they were in the minors.
Devers: 26/39 SB/SBA, .667 SB% in milb, 5/7, .714 in MLB. (406 ml games, 179 MLB games)
Bogaerts: 17/33, .515 milb, 49/61, .803 in MLB. (379 , 759)
Bradley: 35/58, .603 milb, 47/53, .887 in MLB (305, 671)
Ben10: 26/38, .684 milb, 42/50 .840 in MLB (151, 331)
Vazquez: 15/25, .600 milb, 11/14 .786 in MLB (546, 291)
Swihart: 27/40, .675 milb, 10/14 .714 in MLB (421, 191) He was 6/7 in 2018 though.
Total w/o B: 146/233, .627 milb, 159/192, .828 in MLB (2208, 2422)
Betts: 92/107, .860 milb, 110/132 .833 in MLB (299, 644)
It's kind of amazing, really.