The Giants took nearly the same group of relievers into this season as the one from their playoff roster last year, when they were the best in the majors. Come September, the faces have changed, the results have been wildly different, and there is no playoff roster to account for. Thus is the fickle nature of bullpens. Looking ahead to next year, key holdovers from 2021 — Dominic Leone and Jake McGee — are already gone. Others, such as Tyler Rogers and Jarlín García, have assumed lower-leverage roles. One arm, attached to Camilo Doval’s right shoulder, looks like a fixture for years to come. T…