The He 162. If they had been able to develop that aircraft a little bit, and make it out of metal than wood, it might have been a game changer on bomber formations because they could have built scads of them.
Actually it wasn't the wood that was the problem. Note how well the Mosquito did. It was that they were using what amounted to standard wood glue to hold the laminations together, and if it got wet it became ungluded. The plan had been to use an epoxy resin to hold the wood together, but the plant got bombed completely by accident. One of the best misses of the war. It did have a better engine than the 262, but with only 2 x 20mm it was low on fire power against the B17s.