Domestic violence is already seriously under-prosecuted and victims given little protection at all. It's seen somehow as less important than other forms of violence, while I would say that this should be the opposite.
No one with a history of violence should be allowed to own a gun, but especially someone with a history of domestic violence, as that tends to be a pattern and not a one-off incident.
The problem is that it's not "proven"; the only side presenting any evidence is the person seeking the protective order. If you make it an adversarial process so that the subject of the protective order can try to refute claims by the person seeking the order, then sure.
But right now it's strictly one-sided. Most places do require some form of evidence, but that evidence doesn't have to meet normal evidentiary standards, and the evidence isn't being questioned in an adversarial way.
Personally, I'm not comfortable removing rights when the person losing rights can't contest it.
I think you're getting temporary POs confused with permanent ones.
My ex and abuser was convicted of domestic violence charges, and currently owns a gun and has no public record of his crimes. This despite being anti gun and getting it for the sole purpose of scaring me. Proof has nothing to do with it. Courts regularly ignore proof in order to fail to protect victims. If they don't accept criminal convictions as proof, there isn't much they will accept. Don't pretend this has anything to do with a need to prove that someone is a monster before taking away his deadly toys.
For what it is worth, our kids are still fighting to heal the damage he did to them. But he has a right to a gun, so bully for him.