I think the difference here is that we know the interface and trusted developer choices of those apps.
I'm currently using Connect for Lemmy right now and I'm still excited for Sync because I've used it for years.
But each update for Connect so far has been extremely good with quite a few features added. It's also incredibly straightforward to use. So at this point I'm curious how Sync will step into the ring.
Hell, it could have all the same features as Connect, but add previewing with a hold and that'd be an amazing thing for compressing posts. But also Sync can cater to left-handed people like me with its customization.
You've described the exact situation I find myself in: long-time Sync user, using Connect (and honestly enjoying and appreciating it) but anxiously awaiting Sync for Lemmy.