I'm sure your review would be of interest on the Cunard board.
We often get questions comparing the 2 lines so a recent comparison would be very welcome.
Just to clarify Cunard don't use the word casual. Their description is "Smart attire simply means a dress shirt and trousers, skirt and a top, or a cocktail dress. Essentially, choose something along the same vein as you’d wear to a stylish restaurant or the theatre on a special occasion."
I wouldn't be going to the Golden Lion if I was in the Grills. It's a good opportunity to make sure you're happy with your table and meet your waiters and sommelier.
You can check the Dinner menu and pre-order your wine.