That makes sense. What I use in my tumbler comes from a pet store. It is crushed walnut shells that is intended to be cage litter for lizards. It is crushed finer than the walnut shell media you buy specifically for reloading. And cheaper too. The crushed shells are not large enough to jam in a primer hole. But even before I found this lizard litter to use as media, I never ran into a problem using regular sized crushed walnut from a reloading store. You are right, normal tumbler media (walnut shells, corn cob) will not do anything for cleaning out primer pockets if you de-prime first. Neither will the finer crushed lizard litter. Media tends to jam in the primer pockets and cause more trouble than it's are worth. However, with that finely crushed lizard litter I don't experience much of it getting stuck in the primer pockets. I would have to clean a small flake of it out of a primer pocket only one out of 30 or so cases.

I did lots of testing - primed, de-primed, walnut media, corncob media, ultrasonic (both primed and unprimed). My conclusion was that de-priming first serves no useful purpose (for me) and adds an extra step to my reloading sequence (because my Lee Precision dies both de-prime and resize at the same time). When it comes to ultrasonic vs. tumbler, the results are equal. Ultrasonic is more messy and more labor intensive than tumbling. And you have to lay the wet brass out in the sun to dry afterwards. If you include that required drying time, ultrasonic takes longer than tumbling too. If you don't count the drying time (I don't know why you wouldn't), yeah, ultrasonic is faster. But you can't do anything with wet brass, so that's really a false speed increase.

The ultrasonic cleaner will make a small improvement in primer pocket cleanliness if you de-prime first. However, I consider it only a marginal improvement that is nothing to brag about. Maybe industrial strength ultrasonic cleaners would do better at primer pockets, buy my heated 2 liter home model does not.