The question in much of Spiral Knights arsenal planning is: Do you want a general-purpose loadout, or a specialized one? In my view, these split non-normal armors exist to make armor sets that protect against all four damage types, and hence are general-purpose.

For example, the most legendary general-purpose armor set is Divine Veil with Skolver Coat. It gives you all four damage protections, the three most important status protections, another status protection, and two offensive bonuses. (My secondary character plays with this and nothing else.)

On the other hand, if you are a more developed character, who has multiple armor sets for specialized situations, then you may never use a general-purpose set at all. (My main character doesn't.) Instead, you equip armor based on offensive bonuses, or based on piercing, elemental, or shadow damage, with the appropriate trinkets. It's quite an operation.

In Stratum 1, monsters do entirely normal damage, or close to it. As you go deeper into the Clockworks, monsters increasingly deal their preferred damage type (e.g., piercing for slimes). But even on Stratum 6, there is a lot of normal damage being done. So, whatever you do, you should always have some normal armor on.