I loaded 45-70 and 44 spl shells with black back in the 80's. I'd toss the shells in a pan of water and simmer them gently on the stove for a little while, then dump them out on a towel to dry. That's all I ever did, never had a tumbler. I still use some of that brass, after I quit loading black I had a friend with a tumbler clean them, but that was in the 80's also. They seem fine. Some had dark crud inside, but it hasn't hurt so far as I can tell. I think the darkest ones were rounds I shot and didn't clean right away, like when camping.
I've found black powder shells laying on the ground that have most likely been there most of 100 years or so and they weren't corroded away. I doubt brass would be seriously damaged if you didn't clean it at all and kept shooting it.
I think most of our desire to keep brass looking like new is cosmetic more than practical. I didn't have any way to clean brass other than a rag for most of the time I've been reloading and it hasn't ever casued any trouble that I'm aware of. I sort of liked the way the brass discolored over time. Seems today folks feel their brass is damaged or inferior if it doesnt look like new all the time. The rag cleaned grit and dirt off, I've never had dies scratched from not cleaning brass.