I assume lots of contenders have a starter in their rotation with a 6.00 ERA...
I never liked the Taillon signing, but he did give the Cubs a couple solid years of value in the middle two years of the contract. But now, the time has come to move on. Unless there's a minor injury and they can stash him away for awhile on a rehab assignment in case of emergency, he needs to be released by the next time this rotation spot comes around.