There is zero scientific lit that supports the claim that it is as, or even more, important to spend training time trying to increase one's dead lift to 500 lbs than it is to spend training time on long distance runs when training for an ultra marathon.
If I am incorrect on this, show me the study. (but don't waste your time searching)
(and yes, we are all well aware of studies showing people improving more at the 5k when substituting a small amount of leg lifting or plyometrics for aerobic running. However, most or all of these studies did not allow the non-lifting groups to do basic sprints instead of the power training, which under most training programs, they would be doing (not doing just aerobic runs). That might have equaled things out. And a 5k is about 30 times shorter than many ultras, i.e., speed and power matter more in the 5k. Lastly, he said swap out your weekly or bi-weekly long run, a key component of any almost long distance training program, for a deadlift session. Again, show me the study of runners training for an ultra, and one group skipping their weekly long run and doing deadlifts instead, and the deadlift group doing better.)