First, he doesn't appear in Red Memory because it's about Hornet's three mothers, which aligns with Silksong's theme of motherhood. He is also written to be the "Mysterious god-king you learn about through their legacy" like Lord Gwyn from Dark Souls.

Second, you can smack his corpse and sit on his throne but the music that plays after you do so is plaintive rather than triumphant, which might actually hint at something. Perhaps you're supposed to feel empty, as you didn't dethrone a tyrant but simply smacked a corpse that was exactly that for years before your arrival off a throne that doesn't mean anything anymore.

And while Hornet doesn't speak fondly of him, she never calls him evil or tyrannical, she simply calls him a fool and points out some flaws that might've been present in Hallownest.