Thank you very much @Didac and @alex0 for taking the time to write down and share your thoughtful and detailed responses!
Notice I began my message with “I’m trying to understand…” so it is actually explicit that I am very likely to have many things wrong 
I’m not questioning architectural decisions which by now is pretty obvious I don’t quite understand (I imagine and also infer from your explanations that part/most of Logseq’s functionality is made possible precisely through that arquitecture). The thing is… it’s not working for me right now. I really want to love Logseq and eventually use it as my go-to app for notes, so I’ve been testing what for me would be like the essential setup with a laptop and a mobile phone working over the same graph, but I keep experiencing sync conflicts and data loss.
Also I’m far more familiar with the “file representation”. The “graph” and runtime environments… not so much. Which in turn makes it too much difficult for me to try to find out what I might be “doing wrong”—and then fix it.
And that’s where the question came from. Again, thanks again to you both for this conversation! I certainly have some more breadcrumbs to follow now 