1. Not all armor need mods.
1a. The ones that do not need mods are not worse than others, they just pre-defined.
2. Modding let's you keep your favourite looking armor set all the way through the game, while pre-defined armor (non-modable) potentially has better looks at the end-game content.
So do I just keep creating the same armor, but with each tier of skill build one with a better armor class?