The only really bad scenario is if all 3 signer servers get seized at the same time.
If just 1 out of 3 is unavailable, the multisig transaction can't be signed anymore. Unless you mean a 1/3 multisig setup, but that creates other risks.
It is a 3/3 multisig setup, 1/3 would defeat the purpose. The reasoning behind it is that if one signer will ever be seized or it stops for any reason there is no damage that can be done.
That makes sense. My assumption was the multisig is meant to protect against losing access, but it's against someone else gaining access.