You are correct: the benefit isn't due to the different values, but in the fact that they are in parallel, effectively halving the lumped ESR and high frequency inductance. As Mr. Johnson [8.2.4] put it:

The best way to get very low inductance is to parallel a lot of small capacitors.

Different ESR values matter for signals or noise above 10MHz; above 100MHz, only package (lead) inductance matters.

This reminds me of another quote, however, repeated by Donald Knuth:

Premature optimization is the root of all evil.

You are correct: the benefit isn't due to the different values, but in the fact that they are in parallel, effectively halving the lumped ESR and high frequency inductance. As Mr. Johnson [8.2.4] put it:

The best way to get very low inductance is to parallel a lot of small capacitors.

Different ESR values matter for signals or noise above 10MHz; above 100MHz, only package (lead) inductance matters.

This reminds me of another quote, however, repeated by Donald Knuth:

Premature optimization is the root of all evil.