I think it's a case of classic "gameplay and story segregation" honestly. Gale is mentioned to be a former Archmage and Shadowheart can become a Dark Justiciar, none of which are things that can happen at those levels. It's purely a gameplay convention, just like how Halsin's 10 strength is contradicted by a line in the epilogue mentioning him moving stone "three grown men couldn't budge" together.