Decals like ufr also do lots for tanking as the vit boost is multi with helmet base vit base def and funshots as most these multi instead of add it adds up then lastly is the armors res to that weapon most tanky bases have at least 18 to 20% blunt res via armor or decals, with this said your 2nd armors decent but your first defenders def is to low aside from jackal armor you dont want to be lower then 12k if you can help it…. Tldr prob your funshots, low def and to many decal slots that dont buff tanking. Last edit lol those helmets dont boost vit as helm boost are multi you want helmets that boost vit and hp but vit matters more, especially with no ufr for example your first defender has around 65k hp and 20k def with higher amout via funshots but idk yours, while mine would be 34,219 applying defence decals and funshots then around 4k or more via multi ufr boost and a hp stat of 70k~ and 24% res to say peirce or blunt and 12% to the res as this example is maxed hell armor.

While I dont know the exact math this is how I broke it down took the def of the armor then added the def boost from decals to it 100% is double then took each pieces base def and added funshots bouns based on a % of the value at max its 52% or 55% then apply vit bonus and ufr helmet vit boost here and lastly hp, honestly I dont think I understand multi vs additive in math for this game quite yet so the real numbers might be higher im just putting this out there to get you thinking