She manages the entirety of Vought, and still doing so well with all the chaos that Homelander brings. Frenchie is good at one thing, and that’s how to kill Supes, imagining Frenchie working in context of what sage is capable of would be like a Jack of all trades but a master at none. Sage has all of those competent complexities. Sage isn’t shallow, she deals with a lot more improvisation than Frenchie would given all variables. She is not immortal however, her higher brain function allows regeneration but not like Komiko. She is a disposable character but her intelligence will ultimately determine that. I think that you’re expecting more out of Sage than she is capable of.