The G3Xn is newer and current multi effects model unit , the sounds are awesome and fantastic, lot better than the past models, btw the G3 you said is older multieffects model unit
The Overdrive and Distortion have better dynamics, they maybe refined it over the years thats why its better now, Zoom didnt and havent release a new flagship this NAMM 2019 so the G5N, G3N and G3XN where the G3XN im using is still the current flagships, there are also HD reverbs and delays, nice chorus, and Amp and Cabinet simulations sound awesome also, its sounds the best to the extent it doesnt have to contain feature of custom 3rd party IR load, the stock Cabinet Simulation sound good. The Acoustic Simumations sound good and there even a sitar simulation