I don't think you have to worry about flex on dually.
Actually I think I would like more flex on mine, as empty riding it horrible. It come with Wranglers and I can only wonder how much tires can help on stiff suspension.
Just yesterday broke granite slab carrying it in my truck on our terrible roads.
Michelin is trusted and long lasting brand, but the car tires suck in wet conditions, so read the reviews.
I had Discoverer on my F250 and they were really good.
Never had good luck to GY. Never bought them new, but few that come with cars gave me enough headaches to never look at the brand.