It's comparable to making Galadriel a party member in LotR even though Halsin isn't quite that epic.
Funny you mentioned *her* ...
I wonder if actual member of that party wasnt some grey (or white later on) Wizard, who was in compareable level of power.
Gandalf is struggling a lot in LotR. He often loses.
Galadriel on the other hand is portrayed as undefeatable and otherworldly in comparison. That's explains it perfectly. If someone OP in the party just destroys everything it's boring and bad storytelling. That's why Gandalf loses to Saruman and dies against the Balrog. Then loses again against the witch king.
If Galadriel would be de-powered to function as a party member like Halsin would be, their character wouldn't be as convincing or important for the story anymore.
