I think a weighted wristband might help for different reasons. Something weighted enough that makes it uncomfortable to quickly flick your wrist and/or only your arm muscles will give you an incentive to use your body to generate force.
If your body senses that it'll fatigue one link in the kinetic chain too quickly, other muscles and systems will compensate. So you'll end up using more of your hips and body rotation to start the movement to take some workload off the arm. The arm will stay loose until the point of contact which provides the whip action.
As a guy who is still learning to BH loop, I will notice that I still focus on tightening the arm and wrist first to initiate the stroke. This is of course c
ompletely wrong and results in balls going weakly into the net as the tension and power dissipates before the point of contact (especially when I time too early and reach for the ball).
To my monkey brain it makes sense that I need to focus and tense up my arm to prepare to hit the ball. If I isolate my focus to just my arm, there will be less to worry about and less to go wrong, right? (obviously wrong). I played VR TT for a year or so before jumping into the real thing and I could hit fast balls with just arm focused shots, especially since I set the paddle settings to max spin and speed (as an aside, I think this is also one reason why adult players should NOT start on tensor rubbers that can get the ball safely over the net with quality using only arm movements).
So now, even 1.5 years into training, my body still defaults into using arm-initiated BHs. When I'm practicing with my coach, I'm somehow able to override this and have better full body form. But then I watch myself playing games and it's obvious bad form is my default and coached training is just a rare break from it.
So for people like me, maybe it would be a good idea to convince my body that arm-only BH loops are bad through discomfort and/or fatigue. Right now I'm just relying on the psychological 'pain' of missing shots but that's not really a great motivator as gambling science shows us that inconsistent rewards are more pleasurable to the brain (e.g. a slot machine that pays out consistently is less addicting than one that pays out very rarely).