The picture I saw was this one, and it's outright wrong. Quoting from page 51 of Economics of forced labor: "The mortality rate in the Gulag during the war was extremely high. From 1941 through 1945, according to ministry statistics,
1,005,000 inmates died in camps and colonies. As a result, despite an influx of new inmates, their total number declined considerably. Between July 1, 1941, and February 11, 1945, for example, the
population in the camps and colonies dropped from 2.3 million to
1.4 million. Moreover, a high percentage of inmates were sick and exhausted. Even according to official data, the share of camp inmates working in production declined between 1942 and 1944 to
65 to 70 percent, and the share of sick inmates rose to about 20
percent." It's true though that on average the mortality rate was roughly 30% in war years and around 6% during peacetime. That hardly makes them better than even US prisons though. Furthermore, the tsarist deaths are a misreading. Those are deaths per thousands instead of a percentage and the Tsarist ones always performed better then gulags in keeping people alive. I have posted the picture from the sources which uses the tsarists numbers.