Trek 820 to Marlin 5 - is this an upgrade?

My 10 year old son currently rides a Trek 820. He doesn't like trail riding due to hills. Because of this I have changed out the cassette from the stock 14-28T to a 14-34T for this season. I have told him that if he enjoys trail riding more because of this change, I will upgrade his bike after this season. So, my question is, will the Marlin 5 (redesigned for 2019) be much of an upgrade for him over the 820? The difference I see is a lighter frame (1.5 lbs), increase to 27.5" tires with 0.2" increase in width, and finally going from linear pull brakes to hydraulic disc. Will these changes make a difference in his easy single track riding experience or should he stick with the 820?


FWIW, the 2019 Marlin 5 is quite impressive for the price point.