I do not own either one of the bikes under discussion, but I have ridden a little bit on both (unloaded). An LHT is very heavy, even by touring bike standards, and the Trek is a few pounds lighter. That is part of the difference. The 520 also has a somewhat stiffer frame, which results in a livelier "feel". I agree that the 520 is more fun to ride unloaded, but Neil's advice is good: try them loaded.

My touring bike is a Raleigh Sojourn, which is closer to the LHT in terms of weight and handling. It is not a particularly fun bike to ride unloaded, but handles beautifully under load, especially with the front wheel loaded heavily.