It’s terrible on syncing small files and its creators admitted: that’s by design and won’t be changed any soon.
https://forum.syncthing.net/t/really-slow-at-syncing-deletin...
https://forum.syncthing.net/t/really-slow-at-syncing-deletin...
I've been using Syncthing for years to keep thousands of files in sync and it's been working wonderfully.
For me it’s terrible situation as it blocks syncs when you need to get them fast. If the app which main function is to “sync files” can’t do that efficiently because they are small — it’s unacceptable for me. Somehow borg, git, resilio are working with them fine but for Syncthing this is unliftable task. I’m not alone here as Syncthing’s forum regularly gets this topic up. Also I don’t want to work around this somehow as I don’t need another one workaround in my daily routines.
PS: it’s my personal opinion/case and I cannot blame somehow authors of the free and open source tool that they didn’t design it as I would expect — I just use another sync tool which works fine.