Huh? If you are not raiding in Mythic, every healer is viable. If you are actually raiding in Mythic, then Shaman is by FAR the most "non-OP" desirable healer in the healing comp, mainly due to SLT and for its range damage output which is not too bad compared to every other but DP or Hpaladin. Please don't mislead people with such things when you have no clue about what is really happening in the healing meta.
Fun fact : mythic overall healing logs from the last 2 weeks. Monk is officially the worst healer atm. Sham/Hpriest/druid being very close. (oh ofc, don't look at parses because... it's only parses. Max score is far more relevant in statistics)
Can't post warlogs mythic overall HPS cause my account is new but you gotta just check