"Replacing" Constitution with Sanity (from DMG) for the "big six"

[Arkhios]

Well, if you feel it's an important ability score for the game, it might be an option- but how many games genuinely require a Sanity score?
With the exception of games that heavily feature Elder Gods or the Far Realm, it's just not something that's going to come up all that often.

I tend to stay away from Adventurer's League and Pre-made Adventures; I just prefer sandbox homebrew campaigns. Mine does have quite a lot of eldritch horrors, so Sanity is (and has been) often relevant.

That said, I'm aware of what you said. Thanks for input though :)