I agree, either Protect and Immune should be the same ability or they should mean different things. The way that would least upset gameplay would be to set them equal, since it would only change the legal targets of cards that negate/are-regardless-of protect or immune right now.
The third component of this that I mentioned earlier is Ignore:
An ignore ability has four parts:
1. it grants the ignoring card immunity to all cards being ignored
2. it grants the ignored cards immunity to the ignoring card
3. characters not in battle and ignored cannot enter battle (i.e., you cannot choose to bring them into battle and they cannot be targeted by an ability that would bring them into battle)
4. characters already in battle and ignored are treated as though they were not in battle for purposes of determining battle outcome
However, this is not an immune ability it is an ignore ability, and cannot be targeted as the former. Perhaps that is how it should be, but honestly, it is kind of odd that we have 3 different abilities granting the exact same level of protection and none of them can be targeted as the others.