Vagabond8630 I did try Logseq (probably more than 2 years ago) because it is open-source but it did not work for me. Primarily because in my view Logseq is an outliner-based notes app and I simply don't like that style for every note I create. In fact, that I can't choose when to use bullet points really annoys me, but this is of course highly personal. In my view, this should be a simple, core setting of the app. However obviously if you love doing everything in outlines, then this will definitely be your app of choice. Just had a quick look online now and it looks you can mess around with CSS (with partial success?) and there are 3rd party plugins, but I'd prefer not to do that. I don't use custom CSS or 3rd party plugins with Obsidian either.
As much as I think open-source is important, and I truly wish Obsidian would reconsider their decision, it isn't everything to me and I'm not willing to default to options that are open-source, but don't provide me the functionality I am looking for. And do remember, even in open-source software critical bugs/security issues can go unnoticed, like Heartbleed as an example. I try to go FOSS wherever I can but achieving a 100% success rate is currently impossible (for me). You're right, I like Syncthing a lot and I "should" probably use it for syncing my notes too. My choice for using Obsidian Sync was convenience and supporting Obsidian team periodically (which can be done via other options), in other words completely arbitrary and probably indefensible :)