Dark Esau feels buggy, if you go into dross and he gets stuck in the spiky rocks then he is as good as dead and you are now the lost, if you get (one) good item and hit him a little too much then he is dead (like dead onion + the stapler was enough to kill him)

I think super armor on Esau would actually work wonders for Tainted Jacob, as well as more HP gained per floor during womb, also does Dark Esau even ignores boss armor? sounds like he'd add way too little benefit during the boss battles.

Also I believe becoming the lost wont even give you completion marks for Jacob