The WiFi bridge idea from the Macbook is a great idea for sure, but sadly my Macbook does not have an Ethernet port. I'm ok being a little patient though, not a big deal.
As for the Windows 10 WiFi, I would agree there can be any number of explanations if not for the fact that iperf3 works perfectly every time I test it between my Windows 10 PC and the Unraid server. To me, this means the WiFi is working great and the issue lies in software somewhere between Unraid and Windows 10. Maybe Samba, maybe a driver thing, maybe some name resolution thing, maybe ACKs are not getting sent or dropped, I dunno.
I am thinking of also trying a Disk Share instead of a User Share to eliminate that area of possible trouble. I also saw a post about TCP timestamps that helped someone with a similar issue. If I can find that post again maybe I'll try that too.