While you are certainly right that it "doesn't eat up all your lift capacity" it certainly would eat up a very large portion of it. Looking at the 250TL loader for the 40/45hp NHs that have about 2000lbs lift capacity then adding a 665lb
grapple is eating up a full third of that lift capacity and leaves you with only 1345lbs to work with. Compare that to adding a 280lb
grapple which would leave 1720lbs. That is a pretty big difference, almost 400lbs of extra lift capacity. It wouldn't interfer with moving brush but it could certainly limit your ability to move rocks and trees.
WR Long's recommendation, that a loader with only 1300lbs lift capacity such as on a 35hp tractor should be fitted with a RGB60
grapple weighing 567lbs is nuts. That would leave you will only 633lbs of lift capacity or about what a Kubota BX SCUT could lift. That is hopeless if you are moving logs or rocks. I have a 48" 280lb
grapple on a loader rated to lift 2700lbs and it has worked just fine. I can still lift more than a ton with that set up. Costs about half or less than the WRLong RGB too. I love the WRLong design but putting the heavier RGB versions on CUTs just does not make sense. The 48" or 60" RGB2 at 325/365lbs or the Millonzi at 280lbs makes a whole lot more sense for the vast majority of CUT owners who have loaders that lift less than 2500lbs.