I'm no expert DC, but I have made one successful HLD and broken many more.
I think it depends on what the limbs look like prior to reducing weight. If the walls are pretty thick, thinning them is probably the way to go cause you want them thin enough to move during the draw. However, if the walls are already thin enough to move, taking wood off the top of them makes more sense.
I'd really try to avoid making the walls too thin, cause the wood will definitely split there. Trust me.