Yeah, the three things I get out of Obsidian compared to my previous approach of a generic text editor + folder of markdown are:
1. As you mention, I can just shove a todo in a note and then I have a note to query all of these so I can make sure I'm following up on things I should be. For me todo systems came and went but it took integrating at the point I'm keeping records when most "todo" items come in for one to stick.
2. Embedding can be kind of handy. I think there's more places I can use it, but I do it so I can e.g. embed my discussion of a ticket in both my 1:1 notes when reporting to more senior leaders, and also my personal log of what I did that day. It's not like a lifechanging moment but it makes me appear more professional and prepared when I'm not going "Hold on a moment, let me pull that up waits for JIRA to load", or having to search for files to open them up as I'd closed them down to avoid tab overload.
3. Templates. I have some e.g. for standup, for 1:1s with specific people, for a daily/weekly note (which includes some recurring todos in the template, to link back to point 1)
---
For the graphing features, yeah, I take a lot of notes, and a lot of them are leaf nodes apart from a few highly connected ones, and those tend to be stuff like "Weekly XYZ meeting agenda", rather than anything enlightening. Having a leaf node each for each ticket I'm tracking in my system or each day's standup is going to make any diagram an absolute mess.
However, the other thing I do use Obisidian for is my tabletop game sessions. These tend to have much more "stable" entities (Player character X, location Y, Maguffin Z). While I don't personally use the graph there, it at least looks much more sensible there to the extent that I could maybe imagine it makes sense for people using the tool in a creative writing/research context. People find mind maps valuable too, even if that never did it for me, so I can imagine people inclined in that way would appreciate basically hyperlinked mind maps.
---
For the point on whether such a structured note taking system is useful at all, I think it really depends on "Does the number of distinct items you need to keep track of exceed your mental organisational capacity to keep track of them?". When I was just a mid level developer, I never took personal notes. For the "now" period, if I had 4 topics on my mind it was a lot, and that was well within my capacity to keep track of. For longer term keeping, either it was useful technical information for _other_ developers as well and I shoved it in a shared wiki, or it was information about how the feature we're working on is evolving as we work on it, in which case it made sense to keep it recorded in a ticket or document. At that point, there was very little left that was valuable to write down but didn't go into some other shared document bucket.
But once my role changed to one where I am now also responsible for the work of other people, that's when things changed and where I needed a note taking system. It might be a very simple topic and we might have talked about it yesterday, but I have n things I'm working on, plus x team member's and their individual n things, plus things that are upcoming that need to be ready for the team to work on.