I’m surprised you found the R Design thumped and hammered over bumps. Our Inscription (non Pro) has 18″ wheels and is the smoothest riding car we’ve had since a 2001 Citroen C5!
Dealers often inflate the tyres to the Eco setting which can be safely reduced by 5 psi or so.
I know the R Design has the “sports” chassis but having driven one with 20″ wheels, it still rode well, although I found the tyre noise intrusive at Motorway speeds and it tended to “tramline”.
I think you’ll find the Inscription Pro more comfortable.