Sometimes you should really read and follow directions.
Additionally, in order to use the local DNS stub resolver of systemd-resolved (and thus use LLMNR and DNS merging per interface), replace dns with resolve in
hosts: files resolve myhostname
(from ArchLinux Systemd-networkd)
Ugh, I didn’t realize why my Internet was going so slow. Then I looked it up. Yep. Full DNS queries for me. Every time I make a request. Sigh.
At least I learned.