I don't want to let my friend roleplay the archangel raphael
Why? Do you have a reason why he shouldn't get the role?
Because people should be familiar with their characters first.
I feel like that is just an assumption that you have about your friend, which is probably done with a little bit of jealousy that is not healthy. If he is casted as Archangel Raphael then the casting director might have a good reason why and there's nothing we can do but to just support them.
I just don't want people who aren't big into the fandom to get it.
I feel like you're not being supportive and gatekeeping someone from getting the role. Fan or not, if he will have a great performance out of it, then it doesn't matter in the end.