The milk is more like a maranade, nothing more than a liquid to mix the lemon juice and garlic in so the flavors will blend. I don't use it to dilute any flavor from the fish, rather I use it as a "carrier to get the lemon and garlic flavor in. I like to mix a few eggs in as well, that way after I've let them soak for an hour, they're all ready for the bread crumbs and the deep fryer.
On stronger tasting fish like catfish, I trim off all the lateral line before I soak them, so the strong taste is eliminated.....Esox