IIRC Smitsu and Sumeko were only "great healers" in terms of what the White Tower has been doing for millennium. The Spirit/Water/Air form of healing was "only the crudest, most hasty battlefield work". Nynaeve is the first Aes Sedai to heal with all 5 powers in nobody-knows-how-long.

Samitsu's Talent may be strong, but she has been limited, as novices have for so long, by learning what "can" and "cannot" be from women who are NOT her equals in healing. Everything we know about the One Power actually implies that the White Tower has been doing the wrong thing by not letting anyone experiment with new weaves and such, especially at a young age before they believe their restrictions. Remember the Asha'man who believed he couldn't affect anything from a distance, and so he couldn't? By teaching every woman who learns what "isn't possible" they have been negatively imacting innovation for their entire existence. Samitsu may be especially Talented at this "hasty battlefield work" but she doesn't have a patch on Nynaeve, and I don't think she could do Healing that isn't physical.

Now, Sumeko, having spent so much time with the Kin, hasn't been as impacted by the White Tower's regulations. She uses Healing very simliar to Nynaeve's, yes, but does she have the innovation with healing Nynaeve has? In one try (hours long, but her first attempt nonetheless) Nynaeve unraveled compulsion lain by one of the most talented "compulsors" from the Age of Legends. She healed severing by instinct, which has never been done in recorded history OR the AOL.

Each in their own way they are talented healers, but Nynaeve does by instinct things that "cannot be done". She seems the only one able to heal abstract or metaphysical injuries. Perhaps the others could be taught, but I don't think Elayne is the one to judge how good someone is at Healing (her own talents being just good enough to heal a black eye).