Evolution is survival of the fittest. That's not a tautology, it actually says something, namely that the traits which survive and thus propagate tend to be the ones that enable some form of adaptation to its living conditions to the individual. The paper lists a bunch of examples:

  - lactose tolerance
  - immunity and disease resistance
  - lighter skin at northern latitudes
  - metabolism and vitamin D processing changes in response to changes in diet after the rise of agriculture

Not a tautology but a definition.

https://en.wikipedia.org/wiki/Fitness_(biology)

The flip side is everything is being degraded by random mutation.

It's like holding a large ball in place on a hill that sees frequent tremors. If the ball is still halfway up the hill it's being held in place, if it's being held in place it's still halfway up the hill. It might be considered a tautology if you're only working with symbols and ignore all the mechanistics.

Whatever does not survive stops registering in later times; most of the time, what helps survival is retained, and what helps survival is what increases fitness.