This is my result after discussion from this thread:
http://forums.spiralknights.com/en/node/46893
Remove Pierce from cobalt, but increase normal to offset it. Overall its weaker due to only normal armor against Peirce attacks, but good vs all others a little bit more. Also 5* granting low ctr all. Also give it low resist to all statuses. This makes it unique. But not over powered and its now worth perhaps taking vs wolver if you want to be generalist or true multirole player.
As for plate armors, buff normal a little more, and grant 5* ctr med sword attacks, so it is actually not a worthless armor. This makes it a true heavy hitter armor, due to still having the ASD penalty, with a glimmer of positive, since the current armor increase is not worth the loss of attack speed and no bonus compared to Skolver.
I like the idea of making the Plate mail line a harder hitting line. Would definitely make the slow speed worth it, turning you into a mighty glaciar-esque character.
I've always seen the Azure Guardian as being a resist low damage types for all damage types. As in, it's mostly normal defense, with some lower defenses to make it seem more like a jack of all trades. Or maybe normal defense could defend more against other damage types...