All animals have repair mechanisms, humans seem to have better than average. This doesn't prove radiation hormesis but it is inconsistent with the LNT model. The dosimetry for the A-bomb survivors is not good but it is better than in Chernobyl. No measurements were made on anybody either place. It now appears from recent studies that the 1965 estimates are closer to the truth.
Radiation effects depend on strongly on the rate.
Also, the 6,000 radium ingestors had no increase in leukemia despite the huge radiation doses to their bones. The radiation was spread over many decades. The best radiation effects study was the radium dial painters who received their radiation over many decades. In 1925 the radium dial industry forbade painters from touching the brush to their tongue. The dosimetry of the radium dial painters was very good since it is very easy to measure the radiation emitted from the body.