That seems a bit too simplistic. How much bigger is the 18 portion size compared to 10? Are you getting the same dish, just scaled up, or is it a different dish?
Most good restaurants I’ve been to don’t actually have a menu you choose from - you get what’s seasonal and what the kitchen has planned for. The only real inputs are how much you are going to eat and how drunk you want to be at the end of it.
I’ve been to one restaurant in the lower price range that also adopted this concept, though with a twist. There’s not really a menu to choose from, you get what you get, but the waiter will update the blackboard with “what you get if you order now”.
The reason I prefer this is because it tends to focus on what’s seasonal and what is the chef good at.