Yeah, but not just a bit slower. At least 2 orders of magnitude slower in my experience.
Manually limiting it to just one folder at a time by pausing everything else means it takes ~30 seconds to get the first folder syncing (and once it’s syncing, the disk is no longer the bottleneck - it’s the internet bandwidth, which is what you’d expect). When it’s all the folders at once, it can take hours before the sync even starts making progress.
The thing is, that even if the folders were on separate physical drives and there was no disk bottleneck on how many we wanted to scan at once, once they’re all scanned and actually start syncing, the chances are that the network will be the limit anyway*. And once all the folders are ready to sync, I’d still rather they synced one at a time: it’s always going to be more useful to have one file complete and one not started, than two files half finished.
This is obviously how it already works within folders. It would be great if could work this way between folders.
/ * Except where I have unlimited bandwidth and I’m downloading each folder from a different host each of which has limited bandwidth. I guess if you were running a syncthing server in the cloud with 20 folders, each folder shared between the server and 1 machine out there on the internet, you’d want the server to do them all at once. But that’s a very on/off scenario.