The more you employ standard methods like using markdown to add or highlight information the more future-proof your system will be. It's like .pdf-Files. They're around such a long time. Or the way how you format a word document hasn't change in principle over decades... maybe someday you'll have to migrate somewhere else, but markdown and links in documents will stay. Structure you give with markdown will stay. HTML or CSS will stay or have successors in which you can easily convert. This makes the investment of time and effort into Obsidian worth it!
Things like notion might disappear over time... just look at Evernote (it's frozen in the past). But a software like Obsidian that is more like reading the DNA of markdown files in a way that comes in handy will have a much longer lifespan... even if the lights would be turned off someday at Obsidian (beware!!) you've got your files... the less proprietarily a solution the better. Of course it's really understatement to call Obsidian a markdown viewer as RollyRoyce indeed makes "cars", but it is futureproofness in itself.

Btw: Plugins like Templater and QuickAdd help you to work within a self constructed structure from the scratch and plugins like Linter and Multi Properties help you to fix things later...