Cutting off of smoke bush has been praised repeatedly on this site (GW) in the past but what I have observed here as that these grow back all snaky and floppy when this is done. And there is no smoke.

Smoke bush doesn't creep underground. Sumac can be quite invasive, whether you cut the top off or not. British and northern European plant-oriented gardens feature a level of dedication that is completely foreign to many American property owners. The scheme you are talking about could actually involve somebody going in every year and removing the sumac suckers from the beds. Otherwise maybe there is a root barrier, something you could also try yourself if wanting to have the sumac.

"I'm wondering whether it's possible to keep such a planting from getting completely out of control."

We had Rhus typhina in an old field where mowing it to the ground several times a year eventually eliminated it (our goal in that spot.) Right now we are experimenting with trying to keep a clump of it under control. Cutting the margins to the ground annually isn't frequent enough to keep the clump from gradually getting larger in diameter, so we are planning to cut the edges more frequently to see if that will do it. However, we live on a farm. I am not sure that this is an experiment I'd want to conduct on an average sized suburban lot. Perhaps a weekly visit to the area and breaking off all sprouts beyond your limit would do the trick or a bamboo-type barrier would keep it in check?

At this time of year, the stunning set of colors it progresses through makes it a welcome addition to our large property, though it isn't mixed in a bed with other plants. It's also great food and shelter for birds.

I've never seen Cotinus grow back "all snaky and floppy" when coppiced. I do it to C. 'Golden Spirit' and it's a vast improvement. And there are many places around here where you can see it with the purple cultivars with their gorgeous flush of deep purple leaves.

Actually you're doing it to 'Ancot', Golden Spirit being a selling name. And without seeing specimens being compared there isn't anything to base a discussion on. I can only go by what I have seen, and what somebody else thinks they are seeing elsewhere does not cancel that out.