When I say it's a lot less work than making an app from scratch I'm mainly thinking about the UI/UX design which only had to be adjusted in Sync's case. I do lots of UI design for private projects and work, so I know that it's a big part of the workload.

his app account for federation problem/features that aren’t implemented in any other app yet

What do you mean? I'm no Sync expert but I did test out the app and didn't notice any special features. I'm especially interested in instance related tech since that's kinda the USP of my own App, Nemmy.