Suffered Much Loss

[Panch]

Seen a couple posts about this card and its back and forth between its a "battleground" and not if its controlled and in your support area. Well which one is it?

and Gimli's helm from set one. If threats go off, can i assign all of the threats to him and then discard the helm to prevent it?

[Air Power]

I don't have an AR quotation for this, but wounds are assigned one at a time and the helm is not a response, therefore:

You must assign a wound for each threat (if possible), so if you have already discarded the helm, you cannot assign wounds to Gimli (because the wounds are prevented), therefore the wounds must be assigned to another companion (assuming any exist).  If Gimli is your only companion, yes, you will not be able to place wounds.

If you haven't discarded the helm, you can assign a wound to Gimli, but you won't get a chance to discard the helm until after the wound is placed.

[Elessar's Socks]

Controlled sites won't receive the battleground keyword from Suffered Much Loss, as they are no longer "on the adventure path."

You can discard Gimli's Helm and then assign all threat wounds in that skirmish phase to him, preventing them all. If you don't discard the Helm, he can take at most one threat wound (assuming he hasn't been wounded yet that skirmish phase), and the rest cannot be assigned to him.

[Air Power]

Controlled sites won't receive the battleground keyword from Suffered Much Loss, as they are no longer "on the adventure path."

You can discard Gimli's Helm and then assign all threat wounds in that skirmish phase to him, preventing them all. If you don't discard the Helm, he can take at most one threat wound (assuming he hasn't been wounded yet that skirmish phase), and the rest cannot be assigned to him.

You're right.  I went through the comprehensive rules (not that I don't trust you, but this seemed counter-intuitive) and found:

"If a character cannot take wounds, wounds
cannot be assigned to that character. However,
if a card prevents wounds, wounds may still be
assigned to that character"

(page 18)