You need to edit the weightmaps using the node Weightmap Brush tool - Transfer Utility works for things thata re close to the skin, but as you get away from the skin the target mesh may get weights from the wrong place. The spikes would presumably want the same weight as their bases, ideally uniform across the abses and along the spikes' lengths. You may also need to add morphs linked to the bends (JCMs) to keep everything looking good.