I didn’t really get anything from his first post that implied that he knew that already; if anything, asking the question of what devotions can increase the life steal of a DoT spell implied that he didn’t know that and was looking for ADCtH advice. The only way devotions can help increase life steal in his situation is binding a different life steal skill proc to them, or increasing vitality damage (but only in the case of SoC).
TBH it’s incredibly counter-intuitive that ADCtH only affects % weapon damage, especially because skills that proc “on attack” are procced by DoT spells (and debuffs for that matter), which implies that all DoTs are considered attacks and would be affected by ADCtH. Sure it’s addressed in the guide, but there’s little-to-no mention of the importance of consulting the game guide when you start the game.
If anything, just change it to % Weapon Damage Converted to Health and it would prevent a LOT of confusion and headaches. They could keep the current terminology for skills with inherent life steal to make that difference clear.