Many of the lower grade hooks I have seen on originals are all loose. If it's well fitted and casehardened it will never be an issue in your lifetime. Most of the bad rap comes from the lower grade guns, I believe, and guns that have been sorely neglected will often have a poor fit in the standing breech.
I don't take my barrels out for cleaning, so I don't fit these breeches for my personal guns.
Look at the long range target guns, English and Irish, with their standing breeches. The sights are often on the heel of the buttstock for the back rest position. Any wobble in the breech would negatively affect accuracy. But these guns were built very well.