I am a massive rules nerd, but I prefer that the system should enable the story, rather than bolting on kludges to an existing scheme to make it work (d20/5e). Which is what CoC is: simplified Runequest with the Sanity mechanic added. Which is also increasingly recognised as being really ableist...

So instead of Sanity, let's say that meeting the Mythos breaks people's connection to human consensus (with associated mental trauma and ongoing health issues), and have a Humanity / Uncanny mechanism. Increased Uncanny makes it harder to recover Humanity, and acts as a penalty to interactions ...