Reddit and Lemmy have a few different nuances that Sync doesn't properly address. A good example is blocking communities or individuals right from the post menu. Syncs development has been sporadic or at least was when I paid attention. In addition Connect has a few additional features like "hide all above" which is a nice feature to have once you get used to it.
Oh! Neat. Yeah, I'm glad I stumbled upon this thread, because I also felt like Sync hardly updated and I'm trying Connect and Thunder out now and I feel like I'm experiencing Lemmy in a whole new way. I feel bad for the guy behind Sync cause I know he put in a lot of work for the Reddit client.