A better comparison would be the JD3520 to the kubota. The weights will be closer and the features more similar.
I had two tractors with similar HP and about 1000 lbs difference in weight. No comparison for pulling power....the heavier tractor is hands down better. Both run PTO implements equally....but agian the heavier tractor can lift more at both the loader and 3 point due to more ballast (and bigger hydraulic pump too).
The 3520 would spec more similarly, but it's a comfort tractor, and the price will be much higher than a std. L. Personally, price aside, the std L series is much nicer than the 303xe series tractors. If you can afford the extra thousand or two the L usually cost, than it would be the way to go.