The Obsidian Sync (official) plugin isn't very clever with its syncing, it does one file at a time, seemingly new requests for each file.

I recently had to sync a new Obsidian vault from scratch, a vault with thousands of files, and it took minutes to complete because of this, even though most files are a couple of KB at most.

Easy to fix and low hanging fruit, but still an issue for us with many files in our vaults.