I like the general approach to stat-boosing items. Replacing "Set Attribute to X" with "Attribute +X" means that you can't massively boost a character's effectiveness with a single item, eg by giving Aerie the vanilla Crom Faeyr.
However, the Champion's Girdle (+3 Strength, immunity to fear) that replaces the Girdle of Fire Giant Strength (set STR to 22) is a bit underwhelming. By that point in the game, permanent immunity to fear doesn't mean that much as everyone has low saving throws plus there's probably several characters in the party that can cast long-lasting spells that make you immune.to fear. Why not keep things simple and make it a +4 Strength item? Not every item needs to be all that special.