If your method works for you and you are satisfied with the results, you don't need to fix what isn't broke. Only thing you may be missing IMO is you are spending a lot of time and effort that really isn't necessary.
I started reloading in the late 50's and have tried and used just about everything. My mainstay for a long time has been chicken scratch (cracked corn) at less than $10 for 80#'s from the feed store even now days, with any of several "cleaning" agents on hand; or with a 4-5 to 1 mix of white and wild rice with no cleaning agent at all (also cheap in large quantity). The wild rice is oily and the ratio can be changed to get what you want left on the brass.
On exceptionally dirty, tarnished brass I played the wash in lemon water and/or dish soap game for a while, but that and the drying was just too much trouble and time consuming, especially those years I loaded in very high volume. Just leaving them in the tumblers a little longer gets it done without all the bother.
Flash holes I guess depends on the media and the flash holes. I always deburr flash holes on new brass or bought used brass as part of the prep, and I do prefer to remove the spent primer before tumbling. The media's I use just doesn't get stuck in them too often unless I wait too long to change the media out when it gets dirty, starts to break down, or if I put too much cleaning agent in it. The rice has a better chance of getting stuck than the cracked corn naturally, but my media separator shakes most of those out.
Loaded ammo has never stayed loaded around here long enough to worry about powder breaking down, but I whole heartedly agree with stimpy that all brass should get a final inspection before reloading it whether new or fired X times, tumbled or not.
HTH
Larry