You should have been able to get Soroka extra days of rest if you had managed your rotation to make it so.
I think the treatment of Fried in this series is sort of interesting as well. I think it's true that he was the most likely of the starters to play up well in relief (I'd argue for Folty too perhaps) and had experience doing it. But to me, it also seemed like he was as likely as anyone else to put up 7 strong innings in a start.
Prioritizing Keuchel's role as a starter in this series seems really veteran/experience/past season performance oriented. I don't think it really reflects who he has been this year. I would not have been motivated to get him more than one start in this series.
I would actually have preferred to go down with the young guys because they are going to be the core of playoff rotations in the future and also are arguably the best options in the present.
.......
But this is not a "this dumb decision cost us the series."
It obviously did not. Or at least not so far. the starting pitching was good in the first three games. I think Keuchel's start was not a success yesterday, but it also was not a disaster. Still, that was not my preference for who would get a short rest second start.
I feel relatively ok with Folty being the decider the way things have gone for him lately.