I wonder who sets the standards for declaring a model to be "light". Is there a certain weight standard or is it just something used as a marketing technique aimed at a certain segment of the rv purchasing crowd? I know there are a few models that are considered half ton towable but most require at least a 3/4 ton truck. Maybe that is the difference.
Way off subject, but I find the recurring comments about using a fifth wheel for parking and a motorhome for traveling to be nothing more than a personal preference opinion. Having had 2 motorhomes, the last a 40' diesel pusher for 7 years, and 5 fifth wheels thru the years, our preference by a long shot is a fifth wheel. I can hook and unhook our fifth wheel just as fast, and maybe even faster than I could the tow car behind our motorhome. Hooking up the outside connections is no different than a motorhome's. With auto level I can level just as fast also. The big argument is the convenience of having kitchen and bathroom facilities and leveling buttons on the inside which we have found to be not such a big deal. I still have those but I have go outside to get to them, yes, sometimes in not pleasant weather, but not very often. We have put close to 50K miles on the Winslow and done many trips moving fairly frequently. I have never found it to be any more of hassle than when we had the motorhomes.
There are many more arguments for and against that have been covered time and again. Like I said, it's a personal preference.