There's only one universal concept when it comes to grapples that is true for all applications, and that is the heavier the grapple, the less lifting power you have. Everything else is subjective and situational. I don't understand why someone would use up close to 50% of the lifting capacity of the FEL with the weight of the grapple, but that's my reality and obviously not someone else's.
Most implements are limited in their application being task specific, and grapples are no exception. A grapple used primarily to move rocks, boulders, large logs and tree stumps might not be as effective at moving large piles of loose brush. In a perfect world we'd have multiple implements but we often have to pick one and hope that it's a jack-of-all-trades vs. master of one.