It's interesting, you're talking about a syncing system (syncing requires connectivity) and have an issue with requiring access to one of the most convenient sources of connectivity, which is the internet.
We're in a transition time right now. Access to the internet is not always available. It is not always fast. But this time will pass. It makes sense, to me, to design for this future.
> I'm trying to rewrite my own ecosystem one app at a time [...] I must make my own.
I sympathize with this (and good luck!). But I could spend a lot of effort organizing my digital life, but (for me) it feels like I would be a slave to this effort, and what does it get me, really? I spent a long time organizing my digital movie collection; now most films I want to watch are on streaming services. I spent a long time organizing music; now Apple Music and Spotify are much more convenient.
There was an essay from a while back floating around online about the ever-increasing burden of organizing our digital lives. I wish I could find it now, but it really summarized a lot of what I feel about this.