And there is no damn difference between them.
There is approximately 10% difference between them. That means that your 16 CHA character will pass about 1 check in 10 more than your 12 CHA character. That's not a massive margin but it is real margin. The DC for the brain is 10 plus your modifiers. The DC to persuade Kagha is 15 plus your modifiers. It's a 100% harder check so it fails twice as often. DnD is often about stacking the deck. The Guidance buff fro Shadowheart is strong, but not massively so. If you take the Enhance Attribute spell for her at level 2 you can give yourself Advantage on Charisma checks for a full day as long as she has Concentration, which allows you to roll 2 dice and pick the best one. That is a much stronger buff; plus you can use the Harper amulet on another character and have Guidance up as well. Do that and a 25% roll becomes a 95% roll.
