High-temperature superconductivity in pressurized and strained bilayer nickelates has emerged as a new frontier. One of the key unresolved issues concerns the fermiology that underlies superconductivity. On both theoretical and experimental sides, no general consensus has been reached, and conflicting results exist regarding whether the relevant Fermi surface involves a γ pocket -- a hole pocket with dz2-orbital character centered at the Brillouin zone corner. Here, we address this issue by unveiling a Janus-faced role of the γ pocket in spin-fluctuation-mediated superconductivity. We show that this pocket simultaneously induces dominant pair-breaking and pair-forming channels for the leading s± wave pairing. Consequently, the superconducting transition temperature Tc is maximized when the γ pocket touches the Fermi level by balancing the two competing channels. This suggests that superconductivity can emerge, provided the maximum energy level of the γ pocket lies sufficiently close to the Fermi level, either from below or above. Our finding not only reconciles two previously opposing viewpoints on the fermiology, but also naturally explains recent experiments on thin films, including the superconductivity under compressive strain, two conflicting measurements on the Fermi surface, and the optimal Tc near the sign change of the Hall coefficient.