Casuals would also always have a chance to encounter rare monsters and monsters with rare high stats and have a chance at capturing them, it would definitely be a lot harder but possible, which means they could get lucky and capture something very rare they notice goes for a lot of zing on the markets but since they aren't interested in the competitiveness of the game they'd trade it off.
Great question!
Thank you for the detailed answer. I like how you will have different leagues, and have a lot of things for casuals to do as well. I can see myself as a rare monster hunter, instead of grinding for the optimal stats.