One sort of “RPG elements” that never felt like a grind was the StarCraft 2 armory. This gave a real sense of progress in that you upgraded a building and it stayed upgraded. Contrarily, you still needed to go through upgrading your vehicles every mission at the armory building. I get that the campaign armory and research were effectively talent trees, but it felt like there really was some continuity and meaningful advancement as a part of the campaign, rather than just starting over with a Command Center and a few SCVs every time. Because sometimes you get tired of learning Bronze Working every game of Civ.
I thought Age of Empires Online was doing that, but it turns out that you are unlocking the ability to train Wheelbarrows every time you play rather than simply learning Wheelbarrows. There are some permanent upgrades down at the bottom of the tech tree.