Nitrate is between one and two orders of magnitude less toxic than nitrite - look at the scales on the test kits for a heavy hint. An order of magnitude is a 10x change.
But ammonia and nitrite are highly toxic short-term. Nitrate toxicity is long-term. Big difference, huge. Besides, we do not really know that the long-term toxicity seen with high nitrate titers in under-maintained tanks is entirely nitrate's fault, or if it is potentiated or actully solely due to or by the other gunderfunk that is also present and which we do not test for outside of a laboratory with specrtrophotometers and flame photometers. Nitrate is a coal-mine canary, it is an indicator of pollution, not necessarily the sole and entire pollution itself.
Some fish are senstive to nitrates (and associated pollutants) at less than 40 ppm, others can survive a over 100 ppm. There are big species differences there.
HTH