Let's not forget that the Thunderbird's primary role, still, is touring and a lot of changes on this new Thunderbird are tailored to improve that experience.
For example, with a new 20-litre tank, the 500 can do Mumbai-Goa in one full tank but the 350 can better that with a 600 km+ range.
Also helpful are the mounting points at the back for your luggage, refined ergonomics and seats that are designed to be comfier.
With suspension that is reasonably plush in most conditions, I personally found the setup to be comfortable but a few might not.
Either ways, it's much better than the cramped pillion seat where the backrest is a pain in the backside. Quite literally.
Also, be careful whom you place there because it is quite intimate two-up - we'd definitely recommend the prettiest girl around.