OK. This version does it all inside a database, rather than writing to excel.
I loaded in the activities, and paths to store in internal data structures.
It does the 216 routes from start to ARC-013 in .125 seconds
It does 14076 routes for the whole thing in about 3.5 minutes
I renumbered the duplicate activities, so the second ones are effectively orphans.
I haven't cross checked the output.
No sorting, just stores the routes in a text string, and outputs to a csv file when finished.
Bigger than I expected. The output csv for the full graph is nearly 4Gb.
Acer Nitro Laptop i5 processor with 8Gb of memory.
Interesting exercise!