Tobirama also only needs one handseal for all of his displayed techs and less handseals = greater mastery. Tobirama's Suiton has shown to be powerful to rip through the Shinju branches with ease; Mei's suiton couldn't even make a slight dent into Madara's Susano'o ribcage. Mei's speciality lies with her KKG, not the single natures.