Capers is matching personnel (3 wide) as well as run/pass likelihood. If you play base or run heavy, the offense wants to pass. If you play pass first, their run likelihood goes up (see Forte versus the Packers).
And I disagree about the match for the Packers players in a 3-3. There are few, if any, pass rush options to man the three down positions. Raji, Daniels and Jones would be the likely LOS and Jones has struggled mightily versus the run. Raji has not shown his pass rush regularly in a few years.
You need Matthews/Perry and Peppers on the outside for the pass rush alone. As that is job one, you make do if the offense chooses to run. It worked with Matthews in the middle. We'll see this year.