One way to induce insulator-to-metal transitions in the spin-orbit Mott insulator ${\mathrm{Sr}}_2\mathrm{Ir}{\mathrm{O}}_4$ is to substitute iridium with transition metals (Ru, Rh). However, this creates intriguing inhomogeneous metallic states, which cannot be described by a simple doping effect. We detail the electronic structure of the Ru-doped case with angle-resolved photoemission and show that, in contrast to Rh, it cannot be connected to the undoped case by a rigid shift. We further identify bands below $E_F$ coexisting with the metallic ones that we assign to nonbonding Ir sites. We rationalize the differences between Rh and Ru by a different hybridization with oxygen, which mediates the coupling to Ir and sensitively affects the effective doping. We argue that the spin-orbit coupling does not control either the charge transfer or the transition threshold.

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• Electronic structure
• Metal-insulator transition
• Spin-orbit coupling
• Strongly correlated systems
• Angle-resolved photoemission spectroscopy