It seems to me that a TERPS Cat C or Cat D cannot remain in the circling area and get stabilised by even 400ft AGL without exceeding 30° AOB around the base turn, but I'm always learning
Can't comment about category C airplanes (don't fly those) however, I do fly a Category D heavy jet, and the TERPs circling requirement is 2 miles, normally flown at 160 knots, with (in our case) flaps 22, gear down.
The lowest circling minima (under TERPs) is 600 feet for a category D airplane, so...at 160 knots, it is quite manageable.
Note: for the FAA type rating, circling as I have described is
required, otherwise a VFR circling limitation is placed on the license.
...when do you roll out on final ie distance from threshold and altitude...
600 feet, no more than two miles, select landing flaps at this point, and...land.
Is this a demanding maneuver?
Yes, it certainly can be, especially with significant crosswinds, so...I expect many airlines have simply eliminated the circling maneuver, for their own ops.
IE: different strokes for different folks.