I dug into the trade a bit and I don't think it's that bad from CHI's perspective.
First off Hall hasn't played that well, his offensive production is down and his defensive warts are still present from his younger years, I think he has close to no value at his full cap-hit. With full retention at the deadline I could see him being worth a 3rd round pick and if they are lucky, maybe a 2nd.
I would consider CHI getting their own 3rd round pick back (a high 3rd rounder) pretty in line with expectations for a Hall trade, if they retained 50%, but they didn't and on top of that Hall has a penchant for getting injured, so they mitigated that risk in shipping him out early.
What they did do is retain on Rantanen's expiring contract and while on paper you can be like well that's a $9.25M contract and Hall's on a $6M AAV contract, they are clearly retaining more and while that is true in cap terms; but Rantanen is only paid $6M in real dollars this year and Hall is paid $5.25M in real dollars, the end result is a very similar amount of real dollars they are paying out.
I do think prior trade history has shown that teams are willing to retain pretty significant cap-hits on expiring contracts for not all that much trade wise so long as the actual dollars they are taking on are on the low side.
To me this is a Hall trade for CHI, with retention on Rantanen rather than Hall as a small favor. A fair trade for them in my eyes would be getting a 3rd and a 5th round pick, but missing out on a 5th rd pick isn't enough for me to call someone out for being a terrible GM.