First, I think it’s important to define “mobile.” I’m typing this from an 11” iPad Pro. I can pull up Obsidian via a remote desktop solution (Luna Display, in this case) and it looks and works just fine on this device:
In turn, I suspect that Obsidian would work and look great on most tablet form factors. Perhaps limiting the number of panes that can open would be necessary, but otherwise I wouldn’t want to see any arbitrary constraints placed on the app’s design for a tablet.
Phones, of course, are a different story. As @Luhmann pointed out, we can’t assume the user’s use case. I would find equal use in looking up tasks (like Luhmann’s grocery list example), in editing notes, and heck, even writing longform notes with lots of linking (e.g., while stuck in an airport or something).
The phone form factor makes for some complex design decisions, for sure, but the answer to complexity is simplicity—not erasing the complexity. I hate patronizing designs: those that “take care of the user” by limiting what they can do. It is absolutely unnecessary. Look at Numbers, Ulysses, MindNode, or OmniGraffle on an iPhone. These apps all effectively have feature parity with their macOS counterparts, but they allow users to control only what functionality they can access (progressive disclosure). Meanwhile, apps like Mail have key features removed (Mail Rules?), leaving users with confused expectations and frustration that their device-of-choice is being treated as an accessory device. (It seems like nearly every iOS 14 wish list discusses the need for a refresh of Mail.) Evernote is another example of a powerful desktop app that treated (treats? I don’t use it anymore) its mobile users poorly.
Clearly Obsidian’s user base appreciates powerful tools and customizability. Personally, I’m desperate for an uncompromising note-taking experience on mobile devices. C’mon, Obsidian! You can do it!