How much does your bike weigh?

Do your legs not rotate when you pedal?

If you can produce the same power after weight loss, it's always better to lose the weight from body not bike. There are more advantages than just the weight (it's cheaper to lose body weight, you get better heat management, your heart has to pump blood to less tissue so you're more efficient, etc). If you lose body weight you can STILL have a lighter bike too.

Well, I caveated it by stating that I was ignoring any fitness benefits to the weight loss, so it's then just a question of the pedalling thing.

Basically, as your cranks are smaller than your wheels, your feet are turning smaller circles than the tyres, which is where the difference in advantage comes in. Obviously hubs and bottoms brackets offer a much lower benefit than rims/pedals/tyres.