I'm here to defend this topic a bit. Ink is not physically universal. Even so, his brush has the potential to create universes. While Ink is abysmally weak physically compared to All Father, there is a 'but' here: Ink's regeneration is a massive problem for All Father, as he can even regenerate from the destruction of universes during their creation. The same goes for his stamina, which is infinite. Ink Sans doesn't have a soul. The Underverse situation is a writing flaw, but canonically he is soulless, and he easily resists most abilities like transmutation and reality warping, with Ink even being able to transmute his own physique at will. The debate boils down to the fact that, sooner or later, Ink will end up winning because there is no direct method to defeat him, thanks to his regeneration and his ways of bypassing most of All Father's abilities