Six more data points from two PCs:
ran the case, found that excel was 2016.32 despite both windows and license being 64bit. reinstalled office to 64bit, ran again, downloaded 1909 excel update with an interesting message from MS and reran.
ran on an ultra-low-voltage intel laptop with office2019-64bit.
also checked the effects of memory speed, and tried to level the field (board only goes as low as 2.7GHz).
Ryzen1700-3.9GHz-8core-16thread-16GB-DDR4-3200-Excel2016-32bit-179sec - ran only 1 thread
Ryzen1700-3.9GHz-8core-16thread-16GB-DDR4-3200-Excel2016-64bit-87sec - ran only 1 thread
Ryzen1700-3.9GHz-8core-16thread-16GB-DDR4-3200-Excel2016-1909-64bit-68sec - ran only 1 thread
intel i5-3439Y-2.0GHz-2core-4thread-4GB-DDR3-1600-Excel2019-1908-64bit-202sec - ran on 2! threads
Ryzen1700-3.9GHz-8core-16thread-16GB-DDR4-2133-Excel2016-1909-64bit-76sec - ran only 1 thread
Ryzen1700-2.7GHz-8core-16thread-16GB-DDR4-1600-Excel2016-1909-64bit-90sec - ran only 1 thread
Multithreaded and EnableMultithreaded boxes checked in Options-Advanced