why do we say that the larger lymph vessel are comparable to the veins rather than arteries?

cuz of the thickness of the walls. Arteries are much thicker as they have to cope with the high blood pressure, whereas veins don't

larger lymph vessels - have thin walls and valves - like veins.

Veins have wider lumens than arteries. Veins have thin muscular walls since low pressured blood passes through veins. the walls of the veins however have the same components as in arteries, that is, they have a muscular wall, a connective tissue wall, an endothelium and a layer of elastic tissue.  Since arteries experience higher pressured blood the muscular player is much thicker than the one in the veins. therefore, the lumen of the artery is much smaller than that of the vein. Therefore, since lymphatic materials must pass through lymph vessels having the materials being somewhat large, a wider lumen is needed, like that of the veins.