Old school methods of debuting young arms in the pen before transitioning to the rotation are no longer tried and true; it's all true/false now, no multiple choice. Old pal Daniel Bard bounced around and finally bounced back... but seeing if he could start seemed worth a try at the time. Papelbon found his niche at the back end and never wanted to start again.
I'd have to be a real oxymoron to hope to use the word "consistency" in the same sentence with "relievers". Guys thrive, burn out, find it again, then blow it... eventually losing jobs, before getting new life in another org -- to start their mercurial cycle all over again. Look at Kimbrel: bad in the NL, then great in the first half of '21, returns to the AL and bottoms out again.