As a Dwarf, I burned in sunlight despite wearing a Copper Helmet from Mythic Metals.

Checked your code and saw that you checked against a list of vanilla helmets.

For better compatibility, I'd suggest you use the following and then blacklist any items you don't want to count.

{
  "type": "origins:equipped_item",
  "equipment_slot": "head",
  "item_condition": {
    "type": "origins:empty"
  }
}

No mod compatibility is provided for the mod. If you want it you can expand the list of helmets to include those from the mods you are using.