Revisionist history is awesome. We can take a trip back in the time machine. The year is 2021. The starting rotation out of spring training, in order of appearance, is Kenta Maeda, Jose Berrios, Micheal Pineda, Matt Shoemaker, and J A Happ. Berrios is awesome. Maeda and Pineda are serviceable and will give you a chance to win. Happ made 19 starts before being traded to St Louis with a 6.77 ERA and an ERA+ of 63. Shoemaker made 16 starts before being released and an 8.06 ERA with an ERA+ of 53. I would argue that the DFA starters could be worse than Sim since we have already tried that road and failed. Someone should ask Pete Maki and LaTroy Hawkins if they like the DFA squad they have in the bullpen and say "hey, we want that for the rotation too!"
Currently, Sim has an ERA of 6.49 and an ERA+ of 68. While not good, it's still better than the scrap heap starters that we have picked up in the past and suggested we do again. Given the state of the rotation, until somebody comes up and proves they can replace Sim, you have to keep him in the rotation. One thing to remember is that he has no options left. If you want to shift him directly to the bullpen, he will have to figure it out in the bullpen while on the ML club.
I struggle what you would suggest in the short term while Ryan is likely on the shelf. Stick Sim in the bullpen and do a bullpen day when his start comes up? Do a piggyback with Morris? If you believe a DFA candidate is better, can you identify one pitcher DFA'd or not signed that is better that Sim? I believe Abel is going to do another bullpen session today and then decide when he will go on a rehab assignment as he will have to ramp back up prior to joining the team. Zebby has been better, but he still has not gone more than 5 innings in St. Paul. There are no good answers but IMO leaving Sim in the rotation for now is the least bad of all the possible solutions.