Hey thanks everybody, didn't mean to drop out on ya but I had a little unexpected Covid break and I'm back on it and I believe I have it solved!
Big extra thanks to @cmr and @PhilipDAth for the clues I needed. Hooking the MacBook up directly to the Meraki MS250 did result in getting an IP address almost instantly, no interim self-assigned address. I should have read Philip's response a little more closely as I went off in my own direction researching the SG220s which led me to the Port Fast setting you referenced, although in the SG220 this is referred to as Edge Port, at least in the GUI
I changed the port setting to Edge Port for a couple of the ports, connected the MacBook and Boom! 4 seconds to an IP address, even with these clunky USB to Ethernet adapters
Obvious in hindsight but it turns out this wasn't a problem with the Macs at all. I had noticed that the SG220s were slow to pick up an IP address as well, but I didn't connect the dots
On Cloud 9, this has been a thorn for several months. Wondering if I can pull a Costanza and leave work early on a high note