I'm not sure how BTV calculates those values, but as a Cardinal fan, I can say there is no way they'd trade Flaherty for Arraez. Flaherty produced 5.5 bWAR as a 23 year old and Arraez has 5.9 bWAR in ~2.5 years. The Cardinals won't give him up, he's seen as their young ace. Yes, he was injured, but he came back and pitched at the end of the season so he should be good to go for 2022.
Now, if Arraez was a slick fielding SS.......
The Twins and Cardinals don't seem to match up. It seems like the goal was to use BTV to find a good starting pitcher, thus the LA for JF swap idea. As such I think the trade idea was sound. BTV has very limited usefulness. It is worth a look for comparison sake. I'm a Twins fan and there is no way that the Cardinals accept that trade, although it sure would be sweet for the Twins.
They are betwixt the Rock and hard place. IF they could pull off the deal mentioned above, I would certainly pull the pin. It doesn't seem like Gordon has enough glove for SS, and the team remarkably has some options in the MI. And, while no one likes to operate from a point of weakness, and certainly would not admit it, I doubt anyone in MLB will read the following. Which is, this team is in a tough spot, a sold core of position players but with a non complimentary goroup of pitchers. They also don't have an endless inventory of replacement position players. Meaning they will be soon approaching now or never territory. Not only are they not dealing from a position of strength, they only have so many attractive assets to move. They better get it right the first time.
Granted, you need some bodies to keep around in cae you do add a free agent or whatever, and they can't be any of the guys to drop from adds in the November additions.
I'm not sure if Phil Hughes is out-of-options and could be run thru waivers and if not claimed stashed at Rochester, a la Blackburn in the past. If he is not going to pitch in 2018, I would say move on anyways.
Likewise Ryan O'Rourke. Do you keep him and not Boshers? Surely not both.
Let Gee play the marekt. Make a move if you rally think he is the longman or starter in reserve that you wish. Trevor May, hopefully, will return and fill that job as he works his way back into the 2019 rotation. So Gee.....no.
Turley and Tonkin and Slegers and Duffey. You can keep any, but not all. A couple and still expendable and resigned to minor league contracts, although Tonkin would surely walk, as would probably Turley.
Wimmers has left.
Other spots? Adrianza AND Goodrum? One or neither at this point. Keeping Granite makes Palka expendable. That they didn't call him up for a cup of coffee in September makes him the second going of Adam Brett Walker.
Did the Chargois stock disappear? Like Melotakis, and Zack Jones.....has Luke Bard and Jeff Reed pushed by them as prospects, as well as Curtiss and Moya. You have to wonder if Rosario is necessary to keep on the 40-man. Would someone grab him. Left-handed with promise? But enough promise to spend another year on the 40-man?
In putting together the 40-man, I would ask of the names that will be dropped - IS THERE ANY CHANCE THEY WILL BE A PART OF THE TEAM COME 2019.
Like Vargas. Maybe his payday is Asia. Park is still in the mix and under a biog contract.
And what to do with Grossman.
Pretty bad when you could cut out 15 or so guys with a slice of the knife. The problem is you can't replace them ALL with guys starting at A or AA ball, or who need at least part of a season of seasoning at AAA. Removing some from the roster means other teams can claim them and stash them. Not adding them to the 40-man means Rule 5, and as we saw with Stu Turner and the Reds...you can stash an AA player for a season if you really want that player.