What Obsidian actually adds
Start with what it does not change: an Obsidian vault is a local folder of plain markdown, so everything that makes the plain-files build durable survives intact. Your notes open in any editor, sync over any file-sync service, and would outlive the app itself, which is precisely why this is the natural second home for a life OS: you trade none of the ownership for the upgrades.
The upgrade that matters is links. In plain files, connection is a convention you maintain; in Obsidian it is a first-class object the app maintains for you. Write the week with area links in it and the assembling happens in the background: the health note accumulates every week that mentioned health, the backlinks panel turns a year of weekly notes into an area's readable history, and a thread (how did the money situation develop since spring?) becomes a click-through rather than an archaeology session. The second, smaller upgrade is the Templates plugin: the weekly page stamps itself, dated, from one hotkey.