To be honest, Alan, the year's total output from today's tiny cadre of brass importers would not even equal that of just a single modest-sized importer from the early 1960's. Brass is almost nonexistent today by the standards of that bygone era.
When I first came into the hobby there were dozens of importers, with some offering a range of brass locomotives available on a continuous basis, not simply as one-time runs. While runs of today are sometimes no more than 25 units just as you note, some total runs of long ago reached 2,000-3,000 units...as large as runs of the more popular plastic locomotives today!
Incidentally, back in the days the prices of all but the largest brass locomotives were also little more than those of similar examples of diecast engines offered by Mantua, English/PenLine and Varney. As such, brass was widely purchased and run by a broad range of serious hobbyists, not owned mainly by just collectors.
NYW&B